The ceasefire in eastern Ukraine between Kiev's forces and pro-Russian rebels is largely being observed but is still on "thin ice," an OSCE monitor said Thursday, one month after both sides agreed to the truce.

"The ceasefire holds broadly along the long contact line" in the eastern Donetsk and Lugansk regions, with crossfire continuing in some places but at a lower level, said Alexander Hug, deputy chief of the special monitoring mission the OSCE has dispatched to Ukraine.

Armenian troops killed an Azerbaijani soldier in the latest border clash between the arch-foes locked in conflict over the disputed Nagorny Karabakh region, officials in Baku said Thursday.

"On the evening of March 11 (Wednesday) an Armenian army reconnaissance group attempted an attack on Azerbaijani positions and was repelled after fierce fighting," Azerbaijan's defence ministry said in a statement.

Russian rescue workers on Thursday combed through the incinerated rubble of a shopping mall for the bodies of 25 people still missing a day after a fire ripped through the center, leaving five dead, local officials said.

The emergency situations ministry said it had abandoned hope of finding any survivors after the three-storey building was destroyed in the blaze in Kazan, the capital of Tatarstan 800 km (500 miles) east of Moscow.

Russia on Wednesday said it was kicking off a "year of friendship" with totalitarian North Korea as ties with the West languish over Ukraine.

The foreign ministry in Moscow announced it had agreed to start a program of cultural exchanges with the Stalinist regime in Pyongyang aimed at taking ties between the one-time Cold War allies to a "new high level."

Moscow said Wednesday it was baffled by fresh sanctions imposed by Washington on Crimea's biggest bank and a Russian nationalist group, calling the move a "political provocation."

The U.S. Treasury released the new blacklist, which also included eight pro-Russian separatist leaders operating in eastern Ukraine where a ceasefire is seen as largely holding despite sporadic clashes.

German Chancellor Angela Merkel won't attend a May 9 Victory Day parade in Moscow but will visit the Russian capital a day later, her office said Wednesday, amid tensions over the Ukraine conflict.

Merkel has declined an invitation to attend the Red Square commemoration marking 70 years since the capitulation of Nazi Germany to Soviet forces, a government spokesman said.

NATO head Jens Stoltenberg said Wednesday he was "disappointed" by Russia's decision to quit the landmark Treaty on Conventional Forces in Europe as arms control efforts remained important to all sides.

"We are disappointed by the Russian decision to suspend participation in the joint consultative group of the CFE," Stoltenberg told a briefing at NATO's European military HQ in the Belgian city of Mons.

Russia said Wednesday it was ready for talks on a new agreement to control conventional arms in Europe, a day after Moscow said it was quitting the Treaty on Conventional Forces in Europe.

"We are ready to consider the possibility and conduct relevant talks about a new agreement which would meet new realities, would not be too costly, would be well thought-out, measured and which would take Russia's interests into account, naturally," a top diplomat, Mikhail Ulyanov, told the Interfax news agency.

A former Chechen police officer who admitted taking part in the murder of Russian opposition activist Boris Nemtsov "likely confessed under torture", a member of the Kremlin's human rights council told AFP on Wednesday.

Zaur Dadayev allegedly confessed and was charged but has now insisted to the council's Andrei Babushkin that he is "innocent" and only made the admission under duress.

A prominent ally of slain Russian opposition leader Boris Nemtsov on Tuesday dismissed suggestions by Russian investigators that he was murdered because he was anti-Muslim.

Mikhail Kasyanov, who was President Vladimir Putin's first prime minister before joining the Russian opposition, told a media briefing at the European Parliament that Nemtsov was tolerant of all minorities and religions.