Dutch air crash investigators said Monday they expect to release an initial report into what brought down flight MH17 over Ukraine with the loss of 298 lives "in a few weeks".

There were 193 Dutch citizens aboard the Malaysia Airlines 777 when it exploded over strife-torn eastern Ukraine on July 17 and the Dutch are in charge of victim identification and probing the cause of the disaster.

Russian President Vladimir Putin said he believed there is sufficient good will to resolve the Karabakh conflict as he hosted Sunday the leaders of arch-foes Armenia and Azerbaijan.

At the meeting with Azerbaijan's President Ilham Aliyev and Serzh Sarkisian of Armenia, Putin expressed satisfaction that both leaders had expressed their commitment to seek a peaceful resolution of a conflict that has dragged on for a quarter of a century.

Hollywood tough guy and musician Steven Seagal played a weekend concert in the Black Sea peninsula of Crimea, appearing on a stage adorned with the flag of pro-Russian separatists in Ukraine.

Ukraine is ready to accept an aid mission to the eastern rebel stronghold of Lugansk, President Petro Poroshenko said, but only if it is an unarmed international team entering the country through Kiev-controlled borders.

In a phone conversation with German Chancellor Angela Merkel, Poroshenko said he was already in discussions with Red Cross chief Peter Maurer over such a possible mission.

The West warned Russia on Saturday that any attempt to enter Ukraine on "humanitarian" grounds would be considered an "illegal" invasion after Kiev claimed Russian troops had tried to cross the border in the guise of aid workers.

Moscow denied the claim, saying "Russian troops made no attempt to penetrate" Ukraine, where pro-Russian rebels in the east admitted that their stronghold Donetsk had been surrounded by Kiev's troops.

Any "humanitarian" mission by Russia into Ukraine would be "unjustified and illegal", U.S. President Barack Obama and British Prime Minister David Cameron agreed during a telephone call Saturday, Downing Street said.

"On Ukraine, both expressed grave concern about reports that Russian military vehicles have crossed the border into Ukraine and that Russian armed forces are exercising for a 'humanitarian intervention,'" a statement from Cameron's office said.

Russia denied on Saturday that it had attempted to send troops across the border under the guise of a humanitarian mission, and pledged it would not make such a unilateral intervention.

"Russian troops made no attempt to penetrate" into Ukraine, Russian President Vladimir Putin’s spokesman Dmitry Peskov was quoted as saying by Interfax news agency.

Russia said Saturday that it had chased away a U.S. submarine that had approached its territorial waters in the Barents Sea.

A representative of the naval headquarters told Russian news agencies that what was believed to be a Virginia class fast attack submarine was discovered close to Russian territorial waters on Friday.

Russian President Vladimir Putin began talks on Saturday with the leaders of arch-foes Armenia and Azerbaijan after recent clashes that have left 22 soldiers dead and fueled fears that one of the bloodiest post-Soviet wars is restarting.

Putin held separate talks at his residence in Russia's southern Black Sea resort town of Sochi with Azerbaijan's President Ilham Aliyev and Serzh Sarkisian of Armenia. A trilateral meeting was due to be held on Sunday.

Fears mounted Saturday in Ukraine of a possible Russian invasion in the guise of a "humanitarian" mission to the conflict-torn east where Kiev said another 13 of its troops died in fighting with pro-Moscow rebels.

The United States has warned that any unilateral intervention by Russia, including in the form of a humanitarian mission, would be considered an invasion.