A cease-fire seems to have held throughout day-time hours in eastern Ukraine, despite sporadic skirmishes and an overnight shelling of the city of Donetsk.
Witnesses said Ukrainian positions in the rebel-held city were hit by mortar and rocket fire four times during the night.
One woman was injured in the fighting, the Donetsk city council told The Associated Press.
Skirmishes have also been reported near the port city of Mariupol.
Ukraine's National Security and Defense Council spokesman Andriy Lysenko said five Ukrainian servicemen have been killed and 33 wounded since the cease-fire took effect last Friday.
Both sides blame the other for violating the truce.
Pro-Russian separatists have released 648 Ukrainian prisoners-of-war so far under the terms of the cease-fire, Lysenko said on Tuesday.
He told a daily briefing the Ukrainian side was working to secure the release of about 500 more POWs. He did not comment immediately on how many rebel POWs the government side would hand over under the truce deal.
Ukrainian President Petro Poroshenko said Monday that the release of about 1,200 POWs had been secured. Lysenko said the president's figure had referred to the total number of POWs and others believed to be held by the separatists.
Putin weighs in
Russian President Vladimir Putin said Tuesday that he is committed to peacefully resolving the Ukraine crisis, as the United States said it was finalizing measures to broaden sanctions against Russia for its actions againt Ukraine.
The Kremlin’s press service reported that Putin spoke by telephone with Poroshenko, and that the two leaders focused on shoring up the cease-fire agreement reached Friday between Kyiv and pro-Russian separatists. It said Putin confirmed that Russia is ready to continue to promote a peaceful settlement of the conflict.
Meanwhile, U.S. State Department spokeswoman Marie Harf said Tuesday that Washington is finalizing measures to deepen and broaden sanctions aimed at Russia’s energy, financial and defense sectors. She said a decision concerning sanctions would be based on “what’s happening on the ground in the next few days.”
European Union diplomats will consider broader sanctions against Russia at a meeting Wednesday in Brussels.
Authorities in Russia and Ukraine said Tuesday the cease-fire between Ukraine's government and pro-Russian separatists was generally holding, despite some violations. The two sides meanwhile have been offering rival interpretations of what the peace agreement they signed last week means for the future of eastern Ukraine.
Also Tuesday, Russia said it hoped that talks on the status of separatist-held areas in eastern Ukraine would start shortly between Kyiv and the rebels.
"We are hoping that the talks will start quickly," Russian Foreign Minister Sergey Lavrov said, also urging Ukraine to conduct constitutional reforms that would grant its eastern regions greater autonomy.
"Fulfilling agreements is one of key conditions for a sustainable settlement of any conflict," he said, referring to Friday's truce deal.
Kyiv and separatist representatives on Friday signed a 12-point plan in Minsk, Belarus, laying out a roadmap to resolving five months ot conflict that has killed an estimated 3,000 and displaced a quarter million people, according to U.N. figures.
Merkel's blunt words
German Chancellor Angela Merkel, in unusually blunt remarks Tuesday, blamed the crisis in Ukraine on direct Russian involvement, but ruled out any intervention other than sanctions.
“We Europeans have made it clear that it is very, very obvious that under heavy Russian influence – I’ll put it very carefully – including Russian weapons and also troops, Russia is involved in this conflict,” Merkel said in an interview with German broadcaster rbb.
But she said that the only possible response to “Russia’s continuous support [of the separatist movement] in Ukraine” are sanctions which, even taking into account their possible negative impact on Germany’s economy, outweigh the dangers of standing by idly.
The European Union approved a new round of sanctions against Russia Monday but it was not immediately clear when they would be implemented.
Germany is Russia's biggest trading partner in the EU.
Russia pledges support to its companies
Prime Minister Dmitri Medvedev pledged support to Russian companies impacted by Western sanctions, regardless of the ownership structure.
“This is the government's responsibility - to protect Russian business if it is facing unfair and unlawful actions by foreign states or foreign companies,” Russian news agencies quoted Medvedev as saying.
Russian fly-over in dispute
Separately, Russia's Defense Ministry rejected Canadian complaints that a Russian aircraft flew low near a Canadian warship in the Black Sea on Sunday.
Russia's Itar-Tass news agency quoted ministry spokesman Igor Konashenkov as saying Russian aircraft were in the area but did not approach the Canadian vessel.
Some materials for this report provided by Reuters, AP and AFP.