What's been happening in Russia? BBC Security Correspondent Frank Gardner explains

There's been a lot going on in Russia recently, with dramatic scenes that saw the power of Russian President Vladimir Putin threatened.

Last weekend, an army of mercenaries - or privately paid soldiers - known as Wagner, marched towards the Russian capital of Moscow in an armed rebellion.

In response, President Putin ordered the arrest of the leader of Wagner, a man called Yevgeny Prigozhin, saying that he and the Wagner mercenaries had betrayed Russia.

We asked the BBC's security correspondent Frank Gardner to explain what happened, and what that could mean for the war in Ukraine...