President Vladimir Putin has made a bullish speech to top Russian MPs, daring the West to have a go at defeating Moscow on the battlefield.

"What can you say, let them try," he jibed.

The Russian leader also claimed his side had barely started its offensive in in earnest.

His reasoning offered a glimpse of what could be Moscow's wider strategy: the longer the war drags on, he claimed, the harder it will be for the other side to negotiate.

In Ukraine his forces have continued their slow push into the eastern Donetsk region, where a missile strike left at least one civilian dead on Thursday.

Russia has turned its attention to Donetsk after capturing the last city in neighbouring Luhansk - which, together with Donetsk, makes up the Donbas.

But in the south, there was some progress for Ukraine.

The country's flag was raised once more on Snake Island, which was taken by the Russians at the start of the war. It became famous after the Ukrainian border guards stationed on the island told a Russian warship to "get lost" - although in far cruder language.

Russian forces left the island last month.

President Volodymyr Zelensky has paid tribute to outgoing UK Prime Minister Boris Johnson, who was made to step down after a mass revolt by his own ministers.

"Not only me, but also all of Ukrainian society which sympathises with you a lot," he is reported to have said to the British politician in a phone call - thanking him for the "decisive action" he has taken to help Ukraine.

"We have no doubt that Great Britain's support will continue, but your personal leadership and charisma made it special."

He and Boris Johnson had developed a close relationship since the start of the invasion in February, with the UK politician among the first international leaders to visit Kyiv back in April.

However, in Russia - which has been angered by Mr Johnson's support of Ukraine - the reaction was very different.

More than 21,000 war crimes in Ukraine - but could Putin be prosecuted?

Ukraine says it is now investigating more than 21,000 war crimes and crimes of aggression allegedly committed by Russia since the start of its invasion.

Prosecutor General Iryna Venediktova told the BBC she was receiving reports of between 200 and 300 war crimes a day.

Russia, which invaded Ukraine on 24 February, denies all war crimes allegations.

But Ukraine has already jailed one Russian tank commander for war crimes after he admitted shooting 62-year-old Oleksandr Shelipov in the head, a few days after the invasion began.

However, prosecuting those giving the orders higher up - or even Russia's President Vladimir Putin - would not be an easy task.

Our legal correspondent Dominic Casciani has taken a closer look at what it takes to prosecute someone for war crimes, and why bringing a successful case against President Putin is unlikely ever to happen. (BBC)

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