Russia is sending humanitarian aid to Ukraine's conflict-hit east with the help of pro-Kremlin rebels, foreign minister Sergei Lavrov said on Wednesday, the first time Moscow has explicitly acknowledged links to the militants.

"In late May we applied to the (Ukraine) authorities with an official request to get permission to deliver such aid," Lavrov told OSCE Secretary General Lamberto Zannier in Moscow, reported the Interfax news agency.

Russia and Ukraine began fresh EU-brokered gas supply talks Wednesday, with Moscow extending a cut-off deadline to next week in the latest signs the worst East-West crisis in years may be easing.

The negotiations are being closely watched to see if they confirm recent signs that both sides want to bring some sort of closure to a crisis that began with pro-EU protests in Kiev six months ago.

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.

Ukraine's new President Petro Poroshenko has ordered the creation of humanitarian corridors to allow civilians to escape the war-ravaged east for other parts of the country, his office said Tuesday.

"In order to avoid new victims in the zone of the anti-terrorist operation, the president has ordered the responsible ministers to bring about all necessary conditions for civilians who want to leave," it said in a statement.

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.

From international observers and journalists to pro-Ukrainian activists, priests and ordinary citizens, cases of arbitrary detention and abductions are on the rise in the areas of eastern Ukraine controlled by pro-Russian rebels. 

"Kidnappings began from the very beginning of the insurgency and today we estimate the number of those being detained illegally at 200," Maria Oliynik, an activist with Ukrainian rights watchdog Prosvita, told Agence France Presse.

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.  

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.