Frank Gardner
Security correspondent

That depends on how Russia responds.

When things went badly for Moscow earlier on in this war, or whenever the West publicly contemplated supplying Ukraine with more powerful weapons, then President Putin liked to remind everyone that he controlled the world’s biggest arsenal of nuclear weapons.

Russian military doctrine sets out a number of scenarios that would call for that arsenal to be deployed - the most relevant one here is "if the Motherland is threatened".

Ukraine’s surprise incursion into Russia does constitute the first time a foreign army has invaded that country since 1941 but this is not a march on Moscow; Ukraine has made it clear it that this is only a temporary measure.

It is a strategic ploy by President Zelensky to both bring the war home to Russians and better position his country for when the time comes to negotiate a peace deal in earnest.

Putin has vowed "a fitting response" but he knows what Nato’s red lines are and for now, he is likely to focus on punishing Ukraine and possibly stepping up cyber attacks on its Western allies.

Ukraine has put the prospect of peace talks "on a long pause" by attacking the Kursk region, Russian's foreign ministry special envoy says.

Rodion Miroshnik also calls Ukraine's incursion is a "terrorist action".

What we know about incursion from footagepublished at 10:31 British Summer Time 14 August

10:31 BST 14 August

It’s been a week since Ukraine launched its largest and most significant incursion into Russia since the full-scale war began in February 2022.

This isn’t the first incursion into Russia’s territory from Ukraine, but it is the deepest and most sustained seen so far.

BBC Verify’s Olga Robinson has been looking at the latest footage emerging from Russia’s border region of Kursk:

In the last hour, the governor of Russia's Belgorod region has given more details on the latest Ukrainian attacks. Vyacheslav Gladkov lists a total of 23 drone attacks over the past 24 hours, including:

• A drone was shot down over the Alekseevsky urban district where shrapnel damaged seven houses and one outbuilding
• Two cars and someone's kitchen burned down as villages and a town in the Belgorod district were hit by shelling and nine drones - although three of the drones were shot down by air defence systems, he says
• Eighty-four munitions were fired and there were five drone attacks in the Grayvoronsky urban district, damaging two private houses, a church and an administrative building

• And one civilian was hurt in the Shebekinsky urban district as a result of a drone attack. An apartment building, four houses, two trucks and a gas supply line were also damaged in the area

Image source, Reuters

Thomas Copeland
Live reporter

People living in Kursk are "scared to speak even about their feelings" because of fears their messages are being read and monitored by the authorities, says a Russian man from the region.

Nikita, whose name has been changed to protect his identify, tells BBC's Ukrainecast that his family "wake up with the sirens and they go to sleep with the sirens" and they heard a bomb strike a building.

Nikita left Russia four years ago, but his family and friends still live in Kursk.

He says the incursion has not changed Russians' views on the war - including his parents who are still supportive of Putin's invasion.

"I think it depends on what people believed in the first place," he says. For those who blame the West, "I think it proves their point to themselves".

"I am scared for my family. I am worried about them," he says, "but unfortunately, it's out of my reach".

Sir Alex Younger, the former head of the UK's foreign intelligence service MI6, says Ukraine’s incursion is a "very, very bold manoeuvre" that’s "paying off" at the moment.

He says President Volodymyr Zelensky's strategy is that he needs to "reset the politics" of the war to his advantage - and "impose cost and uncertainty on Russia".

He tells BBC Radio 4's Today programme there are still important questions over Zelensky's plan for the logistics and withdrawal in this operation.

But he says Ukraine's manoeuvre is all about making Vladimir Putin realise that "if he keeps on battling against Ukraine, this is going to happen more often".

Frank Gardner
Security correspondent

Image source, Reuters

There will be those on the more cautious end of the spectrum who will argue that Ukraine has already made its point - that Putin’s war of choice must now bring some pain to Russians, that despite recent setbacks on the battlefield in the Donbas, Ukraine has shown itself capable of mounting a sophisticated, combined arms assault using all the elements of modern warfare.

In other words, withdraw now with honour, having given the Kremlin a bloody nose, before Russia brings in enough forces to kill or capture the invading Ukrainians.

But withdrawal would negate two of the apparent objectives of Ukraine’s incursion - namely to put enough pressure on Russia that it is forced to divert some of its own troops in the Donbas and secondly to hold enough Russian territory to use as a bargaining chip in any future peace negotiations.

"If Kyiv holds Russian territory," says Exeter University’s Dr David Blagden, "it can bargain for the return of its own territory from a position of greater strength."

• More here from Frank

Away from Russian territory for a moment, over in Ukraine the country's air force says it shot down 17 out of 23 Russian-launched drones overnight. Russian forces also launched two guided missiles, they add.

The drones were downed over Kyiv, Kharkiv, Kirovohrad, Cherkasy, Mykolaiv, Sumy, Zhytomyr and Zaporizhzhia regions, the air force says.

Infrastructure was damaged in the northern regions of Chernihiv and Zhytomyr, and two homes hit in Mykolaiv in the south - but no casualties were reported.

And in Kyiv, governor Ruslan Kravchenko says debris caused a forest fire which has since been put out.

Image source, Reuters

More now on the remarks by US President Joe Biden last night, as he says he's been briefed every four to five hours for the last six to eight days on Ukraine's action.

"It's creating a real dilemma for Putin," Biden said in his first substantive comments about the operation.

He told reporters during a visit to New Orleans that the US is in "constant contact with the Ukrainians", adding: "That's all I'm going to say about it while it's active."

Earlier this week, the White House said the US had no advance notice of the operation and had no involvement, despite Russian officials suggesting Ukraine's Western backers must have known.

Image source, Reuters

As we’ve been reporting, the governor of Russia's border region of Belgorod has declared a state of emergency - the second region in Russia to do so. Elsewhere:

• Ukraine says it's advancing: Troops have been advancing in the Kursk region of Russia, the Ukrainian military says. President Volodymyr Zelensky said yesterday Ukraine now controls 74 towns and villages in the region - or about 1,000 square km (386 sq miles) according to his military chief
• Overnight drones: Russia says it shot down 117 Ukrainian drones over its territory overnight - including over regions deep into its territory, such as Voronezh
• Russia reacts: But senior Russian commanders claim Ukraine's advance has been halted, with Major General Apti Alaudinov saying "the blitzkrieg that it planned did not work out"
• 'Dilemma' for Putin: In his first remarks on Ukraine’s incursion operation, US President Joe Biden said the attack has created a real dilemma for Russia's Vladimir Putin, who launched the full-scale invasion of Ukraine in 2022
• What next? Ukraine now faces a stark choice over whether to continue its incursion or withdraw, our security correspondent Frank Gardner wrote yesterday

Belgorod is a region in western Russia, near the Russian-Ukraine border.

It neighbours Kursk - where Ukrainian troops launched their surprise attack into Russian territory last Tuesday and where they now control dozens of towns.

Russia has been evacuating residents from Belgorod following "enemy action" near the border. Tens of thousands of people have now left their homes in Belgorod and Kursk since the surprise incursion.

There are currently no confirmed reports suggesting that Ukrainian troops have moved into Belgorod.

Some more developments overnight, and Russia says its air defences destroyed 117 drones which it says were launched overnight by Ukraine.

Russia's defence ministry says several regions, including Kursk, Voronezh, Belgorod and Nizhny Novgorod, were targeted.

It says it also shot down four missiles.

The governor of Russia's border region of Belgorod has declared a state of emergency, saying Ukrainian shelling is making the situation "extremely difficult and tense".

Vyacheslav Gladkov says in a message on Telegram that daily Ukrainian attacks have destroyed houses and killed and wounded civilians.

His announcement comes eight days after Ukraine launched a surprise incursion into Russia. Ukrainian troops have been advancing in the Kursk region of Russia, and Ukraine’s top commander claimed earlier this week that 1,000 sq km (386 sq miles) of Russian territory is under their control.

Francesca Gillett
Live reporter

We're starting our live coverage of the latest from Russia, as Ukraine continues its offensive into their territory.

The incursion started last Tuesday 6 August, with Ukrainian troops entering Russia's Kursk region on the border - an attack that left many surprised.

Since then, Russia says Ukraine has shelled another region to the south - Belgorod - from across the border. Tens of thousands of people have been evacuated from both regions.

My colleagues and I will bring you the latest updates throughout today.