Republican presumptive presidential candidate Donald Trump has tweeted to offer "prayers and condolences" to families of the victims.

Mr Trump was widely criticised for his response to the gun attack at a gay club in Orlando last month in which he referred to apparent congratulations he had received.

Twelve officers were shot in the attack, Dallas Mayor Mike Rawlings has told CBS News, rather than 11 as previously stated by police.

Five of those officers have died.

Mr Rawlings also said two civilians had been shot.

The fourth suspect, who had been in a stand-off with police at a parking garage, is dead, according to the Associated Press, citing Dallas mayor Mike Rawlings.

Here's a breakdown of how Texas law enforcement officers killed in the line of duty died, since the beginning of 2012.

The leading cause of death was gunfire, killing 21 of the 57 officers who died.

Albert Samaha, a US-based reporter for BuzzFeed, has posted a long thread about the Dallas Police Department's efforts to improve community policing and reduce excessive force.

The protest in Dallas at which the gunmen opened fire was a response to the killing of two black men by police officers in Louisiana and Minnesota.

His thread begins with the tweet below.

Jeff Hood, a co-organiser of the Dallas protest, was talking to a police officer at the scene when the shooting started. He spoke to the Dallas Morning News about what happened next.

Here's an image, via AP, of protesters passing through the junction where the attackers later opened fire at police officers.

Image source, AP

Dallas Mayor Mike Rawlings gave an emotional speech earlier in which he paid tribute to police officers who "put their life on the line every day".

Here's a clip via the Associated Press.

Dallas police now have to deal with a sprawling crime scene in the heart of the city. A large area has been shut down, with no access for cars or members of the public. 

Police have already conducted primary and secondary sweeps for explosives, after one suspect claimed to have planted devices in the area, but found none.

Video footage showed that the shooting, which began as sniper fire from elevated positions, spilled out onto the street around El Centro College. 

The streets were closed at 05:00 local time and will remain closed until further notice, police say.

Image source, Dallas City Hall

A larger image of the map is available here, external.

A second victim of the shootings has been named by his family as Patrick Zamarripa, although police have not officially announced the name. Only one of the victims has been officially identified so far. 

A Twitter account in the name of Patrick Zamarripa has tweeted frequently about working for Dallas police. 

The BBC has not verified the authenticity of the account, but photos appear to show the same man as the one pictured above.

The profile picture shows him carrying a baby boy. In one of his recent tweets he celebrated Independence Day, and in another posed with the actor Cuba Gooding Jnr.

Maj Max Geron, a senior Dallas police officer, has tweeted to say that no explosives have been found in two searches.

Police said they would sweep the area after one of the suspects told them he had planted devices nearby.

The BBC Newsbeat team has more on Mark Hughes, the protester named as a suspect shortly after the attack began. A picture of Mr Hughes tweeted out by Dallas police was retweeted nearly 40,000 times. 

He openly carried a semi-automatic rifle at the protest, which is legal under Texas law.

When he heard he was being sought in connection with the shootings, he turned himself in to police and was later released.

Full story here.

Image source, Dallas City Hall

Dallas Police have closed down a large area around the shooting while the scene is investigated. The closures came into effect at 05:00 local time and will last until further notice.

The closed area is shown in yellow on the map above. "Everything inside that box is closed - there is no way in, no way out of that box," said a Dallas police officer in a briefing.

Listen to the full briefing below.

Fifty-eight US law enforcement officers have died so far in 2016 in the line of duty, 26 of them by gunfire.

That is a significantly higher proportion of shooting deaths than in previous years. 

In 2015, 39 of the 130 deaths were by gunfire.

Here is President Obama's full statement on the Dallas shootings.

President Obama once again addressed the issue of assault weapons being available to members of the public.

He said: "We also know that when people are armed with powerful weapons it makes attacks like these more deadly, more tragic. And in the days ahead we are going to have to consider those realities as well."

He has spoken candidly in the past about his desire to introduce stricter background checks and restrict weapons with high-capacity magazines, but there has been little appetite in Congress to pursue such measures.

Appearing alongside President Obama at the news conference, Donald Tusk, the President of the European Council, said: "I am deeply sorry about what has happened in Dallas. We are with you in this."

"Police in Dallas were on duty doing their jobs keeping the people safe during a peaceful protest," President Obama said.

"These law enforcement officers were targeted. 

"I speak for every American when I say we are horrified and we stand united with the people and police department in Dallas."

Mr Obama went on to say the attack was a "wrenching reminder of the sacrifices [the police] make for us".

President Obama is now speaking from the Nato summit in Poland. He called the attack in Dallas "vicious, calculated and despicable".

He said he was being kept up to date by his staff on the attack and had spoken to Dallas Mayor Mike Rawlings to offer "whatever assistance they may need as they deal with this tremendous tragedy".

President Obama is expected to speak shortly about the shootings in Dallas, from Poland where he is attending a Nato summit.

You can watch his statement live below via the White House stream.