Syrian government forces backed by Russian airpower and allied militias opened a new front against rebel fighters south of second city Aleppo on Friday.

The fresh offensive came as Turkey said it had downed an "air vehicle" of unknown origin that violated its air space close to the Syrian border.

Russia's military intervention in Syria will not save President Bashar Assad, French President Francois Hollande said Friday after an EU summit called for a political transition to a new leader.

"It is very clearly stated that Bashar cannot be the future. We must go as fast as possible to a political transition," Hollande told a press conference after the summit in Brussels.

Russia said Thursday that its jets hit 32 "terrorist" targets in Syria over the past 24 hours, claiming it had eased up its air strikes as allied government forces pushed a ground offensive. 

"The intensity of the sorties by our military aviation has slightly decreased in the past day," Russia's defense ministry said in a statement.  

Russia and the United States said Wednesday that they were close to agreeing a deal to avoid clashes between their warplanes over Syria, as regime forces bombarded rebels near Damascus.

Fighting was also reported on the ground in the northern city of Aleppo, where jihadists from the Islamic State group were advancing against rebels.

Turkish Prime Minister Ahmet Davutoglu on Wednesday warned the United States and Russia against "unacceptable" military and political support for Syrian Kurdish forces fighting the Islamic State (IS) group in Syria.

Turkey earlier summoned U.S. and Russian envoys to warn against supplying arms and support for Syrian Kurdish forces fighting the Islamic State (IS) group in Syria.

Ukraine on Wednesday reported its first military fatality from pro-Russian rebel fire in a month as a fragile new truce in the separatist east faced one of its biggest tests to date.

The military in Kiev said the rebels shot at positions south of Avdiivka -- a northern suburb of the separatists self-declared proclaimed capital Donetsk.

The Islamic State group called on Muslims Tuesday to wage jihad on Russia and the United States, as Moscow announced it had intensified its air campaign against Islamic militants in Syria.

The call came as Russian President Vladimir Putin criticized Washington for refusing to cooperate with Moscow in its Syrian campaign, which is having an increasingly dramatic effect.

Australia vowed Wednesday it will not be "bullied" in the pursuit of justice after a Dutch-led investigation found flight MH17 was shot down by a Russian-made missile fired from war-torn eastern Ukraine.

Among the 298 passengers and crew on board the Malaysia Airlines Boeing 777 who died during a routine flight between Amsterdam and Kuala Lumpur on July 17 last year, 38 were Australian citizens and residents.

The prosecutor for the world's only permanent war crimes court Tuesday formally requested to open the tribunal's first inquiry into alleged abuses by Russia, by probing its 2008 war with Georgia.

In her request to a three-judge panel, prosecutor Fatou Bensouda said a preliminary investigation had found evidence of alleged war crimes and crimes against humanity committed by Russian, Georgian and pro-Russian South Ossetian forces during the brutal, but swift, 2008 conflict.

President Vladimir Putin on Tuesday slammed Washington for refusing to share intelligence with Russia on Syria, accusing it of muddled thinking.

"I believe some of our partners simply have mush for brains," Putin said, expressing some of his strongest criticism yet of Washington's handling of the Syrian crisis.