Two Russian soldiers captured while fighting in war-torn eastern Ukraine are being transported to the capital, Kiev, a Ukrainian military spokesman said on Monday.
Authorities in Ukraine say the sole witness in the killing in Moscow of prominent Russian opposition figure Boris Nemtsov has received death threats.
Russia-backed rebels on Tuesday continued their onslaught on the railroad junction of Debaltseve.
US Secretary of State John Kerry is in Ukraine to show support for the embattled government as the Obama administration weighs sending arms to Kiev to help it fight Russian-backed separatists.
President Vladimir Putin on Monday ridiculed the Ukrainian army as NATO's "foreign legion", ignoring Western pressure on the Kremlin to rein in a pro-Russian insurgency that has gone on the offensive across eastern Ukraine.
Thirteen civilians died when shells hit a trolleybus on Thursday in Ukraine's rebel bastion Donetsk as clashes forced Kiev to abandon its dogged defence of the city's airport in one of the deadliest days of the nine-month war.
Russian President Vladimir Putin on Monday said that the investigation of the MH17 crash site is stalling due to Kiev's constant shelling.
Heavy shelling erupted on Monday near the separatist held town of Donetsk in eastern Ukraine, ending a calm period during weekend parliamentary elections.
The United States is destabilizing the global order by trying to impose its will on other nations, Russian President Vladimir Putin declared.
The conflict in Ukraine has driven more than 824,000 people from their homes, the UN refugee agency said on Friday.
Tens of thousands of people demonstrated on Sunday in downtown Moscow against the war in neighbouring Ukraine.
Activists of womens' rights group Femen staged a topless protest against Russian aggression in Ukraine.
Ukrainian Prime Minister Arseniy Yatsenyuk on Saturday accused Russian President Vladimir Putin of wanting to wipe out Ukraine as an independent country.
Ukraine warned on Friday that it will have to adopt deeply unpopular energy savings measures this winter should Russia fail to lift its suspension of natural gas sales to the West-leaning ex-Soviet neighbour.
The site in eastern Ukraine where flight MH17 crashed two months ago is still too unsafe for investigators to resume the recovery of victims' remains, Dutch Defence Minister Jeanine Hennis-Plasschaert said on Thursday.
Russia will retaliate against a new round of Western sanctions over Ukraine and may block flights through its airspace, Prime Minister Dmitry Medvedev said.
Ukraine's Prime Minister Arseny Yatseniuk branded Russia a "terrorist state" that is solely to blame for the conflict in the east of his country.
President Petro Poroshenko accused Moscow of "direct and open aggression".
The European Union on Sunday threatened Russia with new trade sanctions, but sharp divisions among leaders at a summit in Brussels left the timing of any measures uncertain.
Poroshenko said there would be changes in Ukraine's military top brass because of the events of last week.