Two U.S. F-22 Raptor stealth fighters landed in Poland on Monday, as regional tensions run high over Russia and the conflict in Ukraine.

The arrival of the two planes was aired on TVP Info public television channel. They flew in from their German base of Spangdahlem into the Lask air base in central Poland.

The leaders of France, Germany and Russia discussed the Ukraine crisis over the phone on Saturday and agreed to hold a new summit in the coming weeks, said the French presidency.

Francois Hollande, Angela Merkel and Vladimir Putin once again reaffirmed their support for the "Minsk II" peace measures agreed in February. 

Ratings agency Fitch has lowered its rating for Ukraine saying the debt restructuring deal Kiev struck with a group of creditors was tantamount to default.

Fitch lowered Ukraine's rating of long-term public debt from "CC" to "C," after the deal was announced Thursday because it led to major losses for the bondholders.

A former leader of pro-Russian separatist rebels in eastern Ukraine on Thursday announced he was launching a support network for Russian volunteers who fought in the conflict and the families of those killed.

"A lot of people lost their health, lost their jobs, there are the families of the fallen," Alexander Borodai said at a news conference in Moscow.

NATO on Thursday opened a training center in Georgia as the ex-Soviet country eyes closer partnership with the Western military alliance amid tensions with Russia.

The establishment of the NATO-Georgian Joint Training and Evaluation Center, to be based just outside the capital Tbilisi, is aimed at buttressing the small ex-Soviet country which fought a five-day war with Russia in 2008.

The final report into the downing of Malaysia Airlines flight MH17 over war-torn eastern Ukraine last year will be released in October 13, Dutch investigators said on Thursday.

"The Dutch Safety Board (OVV) informed relatives and the accredited representatives to the investigation that the board will publish the final report on the investigation into flight MH17 on 13 October 2015," the board said in a statement.

Ukraine and pro-Russian rebels on Thursday reported the death of eight people in fresh clashes that erupted despite ongoing talks on a new truce agreement for the separatist east.

Government spokesman Oleksandr Motuzyanyk said seven Ukrainian servicemen had been killed and 13 injured in fighting that centred mostly around the pro-Russian republic of Donetsk.

More than 1,000 NATO paratroopers jumped from aircraft above Germany Wednesday in one of the alliance's largest airborne training exercise in Europe since the Cold War ended, the US army said.

Amid a drive by NATO to boost its defenses in light of the Ukraine crisis, 11 member countries are taking part in Exercise Swift Response at the U.S. training area of Hohenfels in southern Germany. It will run until September 13.

Ties between the EU and Russia remain at their lowest ebb over the conflict in Ukraine, ahead of a series of key talks including a visit by President Petro Poroshenko to Brussels on Thursday.

Renewed fighting in eastern Ukraine between pro-Moscow rebels and Kiev's government forces has made a mockery of a February ceasefire, while the European Union has renewed tough sanctions against Russia.

Ukraine said Tuesday that the leaders of Germany and France had agreed to back "firm" steps against Russia should pro-Moscow rebels hold disputed elections in the ex-Soviet state's separatist east.

A top aide to President Petro Poroshenko said German Chancellor Angela Merkel and French President Francois Hollande had agreed at trilateral talks in Berlin on Monday to a set of "red lines" Russia must not cross.