Kyiv is in talks with Moscow over the return of more than 300 Ukrainian soldiers who crossed into Russia amid fighting with rebels. Both sides disagree over the reason for the border crossing.
Ukraine says at least 300 troops and border guards were forced to enter Russia during fighting with separatists and heavy mortar bombardment along the border.
Ukrainian defense spokesman Andriy Lysenko told journalists on Monday that the forces crossed into Russia for safety reasons, after they became trapped between the rebels and the border. However, Russian authorities insist the troops were seeking refuge.
Much of the fighting is currently concentrated in the region along the frontier. Lysenko said diplomatic negotiations were now underway with Moscow to secure the soldiers' return, adding that Ukrainian troops were close to cutting off rebels in Donetsk from the Russian border and their comrades in Luhansk.
Russia's security service said border guards had allowed 438 Ukrainians to cross at Gukovo, between the Ukrainian Luhansk and the Russian Rostov region, after they agreed to give up their weapons.
"They were tired of the war and wanted no further part in it," Russian border guard spokesman Vasily Malayev told Reuters. He added that 180 of the group were taken by bus back to Ukraine later on Monday, and that the remaining soldiers were being kept in a camp on Russian territory.
Speaking on Russian television, Russian Foreign Minister Sergei Lavrov said Moscow would help facilitate the return of the soldiers, but he suggested they had defected.
"I expect Ukrainian authorities to understand that it is absolutely unacceptable, when Ukrainians ... are forced to fight with their own people, to treat those who refuse to do so as traitors to the motherland," said Lavrov.
Encircling rebel enclaves
Government forces have made steady progress against pro-Russian separatists in eastern Ukraine in the past month.
The large rebel stronghold of Donetsk is facing a siege situation, with Ukrainian soldiers urging civilians to leave as soon as they can. Local officials say troops are also tightening their grip on the rebel-held city of Luhansk - home to 420,000 people - which is currently without water and electricity. Luhansk's mayor said the city was facing a "humanitarian catastrophe."
The United Nations says over 100,000 people have fled from eastern Ukraine since fighting erupted there in April.
Crash site investigations
Meanwhile, an international team of experts has resumed recovery work at the crash site of the MH17 airliner, which was shot down over a rebel-held area on July 17.
All 298 people on board were killed, and now recovery teams are trawling through remains spread over 20 square kilometers. So far, over 220 coffins have been transferred back to the Netherlands.
nm/hc (AFP, dpa, Reuters)
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