More heavy fighting has been reported near the eastern Ukraine city of Luhansk. Government forces have claimed fresh gains around one of the main remaining rebel strongholds.
The Ukrainian defense ministry said on Monday that its forces had retaken several villages around Luhansk, which is controlled by pro-Russia separatists, while at the same time breaking through a rebel blockade and reopening a corridor to the city's airport.
The rebels, though, rejected claims that government forces were now actually in control of the airport.
The pro-Russia separatists, however, did concede that 30 of their fighters had been killed after coming under fire in Alexandrovka, in the east of Luhansk. The defense ministry in Kyiv confirmed that its warplanes had carried out five airstrikes on Sunday.
"The enemy suffered significant losses," the ministry said, without putting a figure on the casualties. This, it was reported, included a strike on an armored convoy, which Kyiv said had crossed into Ukrainian territory.
Rebels claim to have shot down military transport
Also on Monday, the rebels claimed to have shot down a Ukrainian military aircraft. The AFP news agency quoted a rebel spokesman as sayingthey had shot down the plane near Luhansk and that three parachutes had been spotted after the aircraft had been hit. Earlier, a Ukrainian military spokesman said they had lost contact with an Antonov transport plane.
Tensions between Russia and Ukraine also rose after the news of thedeath of a Russian man after a shell hit a Russian border town on the weekend,
with a newspaper citing unnamed source close to the Kremlin as saying that Moscow was considering pinpoint strikes on Ukrainian targets in retaliation.
Ukrainian officials have blamed the separatists for the attack.
Meanwhile, Ukrainian President Petro Poroshenko has claimed that Russian military officers were fighting alongside pro-Russia separatists in eastern Ukraine.
"Information has also been confirmed that Russian staff officers are taking part in military operations against Ukrainian forces," he said, according to a statement posted on his website and quoted by the Reuters news agency.
Merkel meets Putin
The latest developments come just hours afterGerman Chancellor Angela Merkel met with Russian President Vladimir Putin
ahead of the World Cup final in Rio de Janeiro on Sunday.
Chancellor Merkel used the meeting to calls on Putin to use his influence on the separatists to help end the fighting that has killed hundreds of people in eastern Ukraine.
"Both Putin and Merkel stressed the necessity to urgently resume the work of a contact group on Ukraine, possibly in the format of a video conference," said Dmitry Peskov, the Russian president's spokesman. "It is their common opinion that, in order for the contact group to resume its work, a ceasefire needs to be declared as soon as possible."
pfd/kms (Reuters, dpa, AFP)