Relatives of German victims of downed Malaysia Airlines flight MH17 plan to sue Ukraine and its president for criminal negligence for not closing the country's airspace, a lawyer said Sunday.

Elmar Giemulla, an attorney and professor of aviation law who is representing three German families, said he would file suit soon before the European Court of Human Rights in Strasbourg. 

Russian President Vladimir Putin and Japanese Prime Minster Shinzo Abe held telephone talks Sunday amid speculation about whether a visit by Putin will go ahead due to frictions over Ukraine.

Local media reports say Putin's visit to Japan planned for this autumn is now uncertain following Tokyo's sanctions on Moscow over the crisis in Ukraine.

The United States said Sunday it hoped Russia would address concerns about its actions in Ukraine ahead of the G20 November leaders' summit, or Moscow risked further economic isolation.

U.S. Treasury Secretary Jack Lew said following a two-day meeting of G20 finance chiefs "the goal between now and November is for this to be resolved so that these issues are on a path towards improvement.

Mikhail Khodorkovsky, a Kremlin opponent who spent a decade in prison, on Saturday launched a movement to bring together pro-European Russians to challenge strongman Vladimir Putin's grip on power.

Once Russia's richest man, Khodorkovsky was released from prison late last year and is now based in Switzerland. He urged his compatriots to pull together to be able to influence the fate of the country.

NATO's top military commanders are meeting in Lithuania on Saturday to discuss relations with Russia as the warring sides in Ukraine agreed to pull back troops under a new peace plan reached overnight in Belarus.

General Knud Bartels, who chairs NATO's Military Committee, said defense chiefs from the 28 nation alliance are set to review "future relationship with Russia and NATO's military posture".

Russia has delivered a third shipment of aid to rebel-controlled Ukraine, sending trucks carrying water and food across the border, a spokesman for Russia's emergencies ministry said on Saturday.

"The convoy has arrived and is being unloaded" in the rebel-controlled city of Donetsk, spokesman Alexander Drobyshevsky told AFP.

Vladimir Putin is set to attend the G20 leaders' summit in November despite alarm over Russia's actions in Ukraine with host Australia Saturday saying it was the "emphatic" wish of member nations.

There had been question marks over whether Moscow should be invited to the high-powered forum in Brisbane with the brutal five-month conflict that has killed around 3,000 people still unresolved.

Ukrainian forces and pro-Russian militias were due Saturday to pull back their troops from a demilitarized zone created under a new peace plan agreed in marathon overnight talks.

A nine-point agreement thrashed out in the early hours of Saturday in the Belarussian capital Minsk also requires the withdrawal of all "mercenaries" from the conflict zone and an immediate end to hostilities.

Two Russian fighters entered a U.S. "air defense identification zone" two days ago and were intercepted by American F-22 jets near Alaska, military officers said Friday.

The incursion on Wednesday was followed by a second incident on Thursday involving two Russian long-range bombers, which flew into Canada's air defense identification zone (ADIZ) and were intercepted by two Canadian F-18 jets, officers said.

Sweden on Friday said it has lodged a protest with Russia after the incursion of two Russian fighter planes into Swedish airspace.

"The foreign ministry Friday summoned Russia's ambassador in Stockholm to tell him of its protests with regard to this incident," the ministry said in a statement.