That wraps it up from us.

You can still follow the latest developments at bbc.com/news

To summarise what happened today:

• Democrats have opened an impeachment inquiry
• It was sparked by allegations President Trump sought help from Ukraine to undermine Joe Biden
• He's authorised the release of the "unredacted" transcript of his July phone call with Ukrainian president
• That's being made public on Wednesday

BBC North America editor tweets...

Ukrainian President Volodymyr Zelensky said conversations with Donald Trump are "private and confidential", when asked by CNN reporter Alexander Marquardt if Trump indicated that aid for Ukraine was tied to investigating Joe Biden.

Asked if he was happy the call's transcript would be out tomorrow, Zelensky replied: "We'll see."

Former FBI Director James Comey - who was fired by Donald Trump in 2017 - told California TV station KCRA that impeaching the president would let the American people "off the hook".

With impeachment, some of Trump's supporters "would think some kind of coup had taken place," Comey said.

Calling the president's behaviour in office "deeply concerning", he called on the public to "take responsibility" and express their preference by voting in next year's election.

Image source, Alex Wong/Getty Images

Kevin McCarthy, the Republican leader of the US House of Representatives, responded to Pelosi's announcement with a brief statement, saying the speaker "cannot decide unilaterally what happens here".

"I realise 2016 did not turn out the way Speaker Pelosi wanted it to happen," McCarthy said, referring to the 2016 presidential vote. But "this election is over".

"What she said today made no difference... it's time to put the public before politics."

Image source, Chip Somodevilla/Getty Images

That sentiment was echoed by the ranking Republican on the House Judiciary Committee.

Joe Biden became the latest Democratic hopeful to announce his support for an impeachment inquiry into Donald Trump.

Impeaching Mr Trump "would be a tragedy", Mr Biden said. "But a tragedy of his making."

Here's what the rest of them are saying:

Anthony Zurcher
BBC North America reporter

All eyes have been on the US House of Representatives today, but the Senate dipped its toe into the Ukrainian controversy as well, by passing a unanimous resolution calling on the Trump White House to turn over the whistle-blower complaint to its intelligence committee.

The resolution was non-binding, but it could have been scuttled by the dissent of one senator. It could also have easily been blocked by Senate Majority Leader Mitch McConnell. The fact that none of the 53 Republicans in the chamber stepped forward to issue an objection to the language drafted by Democrat Chuck Schumer is noteworthy.

In the past it’s been easy to find congressional Republicans willing to protect the White House from an embarrassing vote. At least for a moment on Tuesday, that was not the case.

Support has been building for such a move over recent months.

But it was the details of the president's phone call with the Ukrainian leader that escalated the issue.

There is now widespread support among Democrats in the lower house for impeachment - more than 145 out of 235 members are in favour.

On Monday night, seven freshman Democrats, writing in the Washington Post,, external said that if Mr Trump had acted improperly in his conversation with Ukraine's president, it would "represent an impeachable offence".

More Democrats came forward on Monday and on Tuesday.

Long-serving Democrat and civil-rights icon John Lewis spoke in support of impeachment proceedings earlier on Tuesday.

He said in an impassioned speech that "now is the time to act... the future of our democracy is at stake".

At the heart of the Trump-Ukraine row is the allegation from Democrats that President Trump threatened to withhold military aid to force Ukraine to investigate corruption allegations against Joe Biden and his son Hunter.

Trump acknowledged freezing the aid package but said he was only trying to get Europe to step up assistance by threatening to withhold military aid.

“My complaint has always been, and I’d withhold again and I’ll continue to withhold until such time as Europe and other nations contribute to Ukraine because they’re not doing it,” Trump told reporters at the United Nations General Assembly.

Following bipartisan criticism of the aid delay, the administration approved the $250m for Ukraine this month.

Liz Cheney, House Republican conference chair, has also reacted to the impeachment inquiry.

The Wyoming congresswoman said in a statement: “As members of Congress, we have a solemn obligation to defend the Constitution.

"Speaker Pelosi and House Democrats have cast aside this obligation in order to launch partisan impeachment efforts against President Trump.

“For months, House Democrats have careened from justification to justification, looking for any excuse to begin impeachment proceedings. Since the president was sworn in, the Democrats have repeatedly attempted to overturn the results of the election and discard the votes of 63 million Americans who voted for President Trump."

This impeachment inquiry is based on merely "news reports of a phone call and a whistleblower", she added.

Image source, Bill Clark/CQ Roll Call/Getty Images

In this context, to "impeach" means to bring charges in Congress which will form the basis for a trial.

The US constitution states a president "shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes or misdemeanours".

The process of impeachment has to be started by the House of Representatives and only needs a simple majority to pass. The trial will be held in the currently Republican-held Senate.

Here, a two-thirds vote is necessary for removal - and this milestone has never been reached in America's history.

• Read more on how it works

Freshman congresswoman Alexandria Ocasio-Cortez - one of the most vocal advocates of impeachment - said on Tuesday "these developments are exactly where we need to be".

Asked by reporters if Democratic leadership had been to slow to move forward with impeachment, Ocasio-Cortez said: "At this point it doesn't matter, we're moving forward with it now. We have to hold this president accountable."

Image source, Getty Images

Here's the moment that Speaker of the House Nancy Pelosi announced she would open a formal impeachment inquiry.

Last week reports said US intelligence officials had complained to a government watchdog about Mr Trump's interactions with a foreign leader, who was later revealed to be the president of Ukraine, Volodymyr Zelensky.

That whistleblower's complaint - which was deemed "urgent" and credible by the intelligence inspector general - has been demanded by Democrats in Congress, but the White House and Department of Justice have refused to provide it.

What exactly was said remains unclear but Democrats accuse Mr Trump of threatening to withhold military aid to force Ukraine to investigate corruption allegations against Mr Biden and his son Hunter.

Mr Trump has acknowledged discussing Joe Biden with Mr Zelensky but said he was only trying to get Europe to step up assistance by threatening to withhold military aid.

He has said his administration would release the full and unredacted transcript of the phone conversation he held with the Ukrainian leader.

• Wait, what's this story all about?

Anthony Zurcher
BBC North America reporter

For months now, Democratic leaders in the House of Representatives have been playing a semantics game. They wanted those who supported and those who opposed a formal impeachment inquiry into President Donald Trump to both think they were getting what they wanted.

This strategy suggested a fear by Speaker Nancy Pelosi and others that heading down the path to impeachment would put moderate Democrats facing tough 2020 re-election fights at risk.

That calculus appears to have changed, after the rapid drumbeat of new revelations about Mr Trump's contacts with Ukrainian President Volodymyr Zelensky. Now even middle-of-the road politicians are coming out in favour of impeachment proceedings.

The dam has broken. The genie is out of the bottle. Pick your metaphor. The simple fact is that Ms Pelosi - a keen judge of the political mood within her caucus - has made the decision to shift from resisting impeachment to -at the very least - being open to it.

The path forward is uncertain. The administration could back way from its across-the board stonewalling and give Congress some of the information it requests. Opinion surveys could show the latest drama is taking a toll on one party or the other, causing political will to crumble. Or, both sides could dig in for a long, gruelling battle that could drag into the darkest days of winter.

Image source, Spencer Platt/Getty Images

President Trump is not in Washington today - he's in New York where he's held a series of meetings with world leaders and delivered a speech at the United Nations General Assembly.

According to the White House pool report, the president is currently enjoying "executive time". He just tweeted his response to Nancy Pelosi's statement.

The former vice-president and current frontrunner for the Democratic presidential nomination is at the centre of this story. Here's the warning he issued to President Trump a couple of hours ago.

Image source, AFP/Getty

Making her remarks, Pelosi said that President Trump has "seriously violated the constitution".

"This week, the president has admitted to asking the president of Ukraine to take action that would benefit him politically," she said.

He has betrayed his oath of office, national security, and the integrity of elections, she added.

The law is unequivocal," she added. "The president must be held accountable."

An attempt to remove Mr Trump from office would require about 20 Republicans in the Senate to rebel against him.

No US president has ever been removed from office by impeachment.