Ukraine crisis: 'Thousands of Russians' fighting in east
A pro-Russian rebel leader in eastern Ukraine has said 3-4,000 Russian citizens are fighting in their ranks.
Alexander Zakharchenko told Russian TV many of the Russians were former servicepeople or current personnel on leave.
He was speaking as rebels captured the town of Novoazovsk and threatened to take the city of Mariupol, after opening a new front in the south-east.
Reports say they are advancing on the city, a key port on the Sea of Azov.
Ukraine says Russian forces have crossed the border and are supporting the rebel attack, but Moscow has repeatedly denied arming or covertly supporting the rebels.
There are suspicions that Russia wants to divert Ukrainian forces from the besieged cities of Donetsk and Luhansk, further north.
Government forces have made significant advances against the separatists in recent weeks.
In other diplomatic developments:
- An "increasing number of Russian troops" are involved in the fighting, the US ambassador to Ukraine, Geoffrey Pyatt, writes on Twitter
- German Chancellor Angela Merkel demands an explanation from Russia's President Vladimir Putin amid the reports of an incursion
- French President Francois Hollande says it would be "intolerable" if Russian troops are in Ukraine, and demands that Russia stop sending aid to the rebels
- The Organisation for Security and Co-operation in Europe (OSCE) is holding a special meeting in Vienna to discuss developments in Ukraine.
Ukrainian forces 'leaving'
Mr Zakharchenko, who is prime minister of the self-declared Donetsk People's Republic, said Russian citizens were coming to Ukraine to fight because they felt it was their duty.
"There have been around 3,000-4,000 of them in our ranks," he said, adding that the rebels' struggle would have been much harder without them.
But he insisted that any Russians fighting on the rebel side were doing so voluntarily.
"Many former high-ranking military officers have volunteered to join us. They are fighting with us, considering that to be their duty," he said.
"There are also many in the current Russian military that prefer to spend their leave among us, brothers who are fighting for their freedom, rather than on a beach."
Ukraine's security and defence council confirmed reports that Novoazovsk had been captured by the rebels, whom they described as "Russian troops".
It said it had withdrawn its forces to save their lives, and they were now reinforcing Mariupol's defences.
A Ukrainian company commander, Vladimir Shilov, told Ukrainian TV that he had heard from sources inside the town that it was blocked by tanks and no-one was allowed to leave. Local officials had already fled to Mariupol, he added.
A spokesman for the rebels told Interfax news agency that Novoazovsk was under their control and they would soon "liberate" Mariupol.
Reports on Twitter suggested the rebels were already advancing towards Mariupol, and rebels said they had captured checkpoints to the west of the city.
The port has until now been peaceful and cut off from rebel positions.
Rebels have been trying for weeks to break out of an area further north in the Donetsk region where they are almost encircled.
Analysts say the separatists could also be seeking a land link between Russia and Crimea, which also would give them control over the entire Sea of Azov.
Russia annexed the Black Sea peninsula of Crimea from Ukraine in March.
War in eastern Ukraine: The human cost
- At least 2,119 people had been killed and 5,043 wounded since mid-April, a UN report on 7 August said
- 951 civilians have been killed in Donetsk region alone, the official regional authorities said on 20 August
- Official casualty counts only record certified deaths while in some particularly dangerous parts of the war zone, such as Luhansk region, victims are said to have been buried informally, for instance in gardens
- Rebels (and some military sources) accuse the government of concealing the true numbers of soldiers killed
- 155,800 people have fled elsewhere in Ukraine while at least 188,000 have gone to Russia
Ukrainian President Petro Poroshenko promised a roadmap for peace in the east on Tuesday after holding his first direct talks on the crisis since June with Mr Putin.
Mr Putin said Russia would assist any ceasefire talks, but that stopping the fighting was a matter for Ukraine alone.