Germany's foreign minister on Tuesday said that all sides appear committed to defusing the conflict in Ukraine following three-way talks with his Russian and Polish counterparts, but Moscow warned there was no sign of the fighting subsiding.

Russia's top diplomat Sergei Lavrov said the Kremlin welcomed Ukraine's decision to establish humanitarian corridors in the separatist east but stressed that Moscow has yet to see an easing in the crisis.

Russia launched military maneuvers on its westernmost edge on Tuesday, a day after NATO began war games near the Russian border that Moscow labeled "an act of aggression," amid simmering East-West tensions over Ukraine.

The Russian defense ministry said military drills involving the Baltic Sea fleet, the air force and paratroopers were under way in Kaliningrad, a Russian exclave sandwiched between EU and NATO members Poland and Lithuania.

German officials will visit Tehran on Sunday for talks on Iran's nuclear drive, top Iranian negotiator and deputy foreign minister Abbas Araqchi said on Tuesday.

The meeting will follow similar discussions with American, Russian and French negotiators this week ahead of the resumption of political talks between Iran and the main P5+1 group of world powers on Monday in Vienna.

The United States is hopeful that after months of attacks and tensions "significant progress" could be made this week to end the fighting in eastern Ukraine, a U.S. official said.

Washington had been "encouraged" by the talks, between Russian President Vladimir Putin and the incoming Ukrainian leader Petro Poroshenko, in Normandy last week, State Department deputy spokeswoman Marie Harf said.

NATO on Monday launched one of its largest military maneuvers in the Baltic states since tensions spiked with neighboring Russia over its annexation of Ukraine's Crimean peninsula.

Around 4,700 troops and 800 military vehicles from 10 countries including Britain, Canada and the United States are participating in the Saber Strike exercises near the Latvian capital Riga.  

Russia on Monday accused the European Union of putting pressure on Bulgaria to suspend work on a key Kremlin-backed gas pipeline, and said eastward expansion by NATO was "counterproductive".

Foreign Minister Sergei Lavrov said EU member state Bulgaria's move to halt work on the South Stream gas pipeline suggested the bloc was seeking revenge over the Ukraine crisis.

A Russian court on Monday jailed two men for life for the 2006 murder of investigative journalist Anna Politkovskaya while handing down sentences of between 12 and 20 years to three others.

Rustam Makhmudov of Chechnya, convicted of firing the fatal shots at Politkovskaya, and his uncle Lom-Ali Gaitukayev, found guilty of organizing the brazen hit, were jailed for life at Moscow city court, Russia's Investigative Committee said in a statement.

Ukraine launched delicate dual-track diplomatic negotiations with Russia on Monday aimed at averting a debilitating gas cut and ending a bloody separatist insurgency by the end of the week.

The meetings in Brussels and Kiev throw down an immediate challenge to new Ukrainian President Petro Poroshenko's European commitment and vow to preserve the territorial integrity of the splintered ex-Soviet state.

Ukrainian security forces have released two Russian television journalists working for a defense ministry outlet after they were detained at a checkpoint in the rebellion-hit east of the country, the channel said Monday.  

The journalists from Russia's Zvezda, or Star channel -- sound operator Anton Malyshev and cameraman Andrei Sushenkov -- were arrested Friday by Ukraine's National Guard "on suspicion of monitoring and collecting information" of government operations close to the rebel bastion of Slavyansk.

Ukraine's new Western-backed President Petro Poroshenko said on Sunday that fighting in the separatist east of the ex-Soviet country must stop by the end of the week.

"We must end the fighting this week. For me, every day in which people die, every day in which Ukraine pays such a high price, is unacceptable," Poroshenko said in a statement published on his official website.