Pro-Russian rebels have opened up a new front in south-eastern Ukraine.
Reports say they have taken the town of Novoazovsk, on the Sea of Azov, and are heading for the key port of Mariupol.
Ukraine says Russian forces have crossed the border and are supporting the rebel attack, but the Moscow government 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.
Government forces have made significant advances against the separatists in recent weeks.
German Chancellor Angela Merkel has demanded an explanation from Russia's President Vladimir Putin amid the reports of an incursion.
The US said it suspected a Russian-directed counter-offensive was under way.
http://www.bbc.com/news/world-europe-28963310
