Syrian Foreign Minister Walid Muallem predicted Sunday that Russia's increased involvement in his country would prove a game changer in the international campaign against the Islamic State jihadist group.

"More important than the supply of arms to Syria is Russia's participation in the fight against Daesh and al-Nusra Front," al-Qaida's franchise in the country, Muallem told Russia Today television, using an Arabic acronym for IS.

German police are investigating an asylum-seeker on suspicion that he fought for the Islamic State group in Syria, newspaper Welt am Sonntag reported Sunday.

The suspect is a Syrian national and lives in an asylum-seeker shelter in the northeast region of Brandenburg, the newspaper reported, quoting security sources.

Nearly 30 migrants were feared missing off the Greek island of Lesbos, the coastguard said Sunday, in the latest boat sinking in an ongoing Aegean Sea tragedy that has cost hundreds of lives.

The coastguard said it had rescued 20 people spotted in the water by a helicopter from EU border agency Frontex, but the survivors said another 26 people had been in the boat.

Thousands of migrants sought their way through a chaotic maze of rumor and proliferating border controls in the western Balkans on Saturday.

In the latest chapter in the EU's escalating refugee crisis, Croatia, Hungary and Slovenia tussled over how to cope with a wave of refugees desperate to reach northern Europe.

U.S. Secretary of State John Kerry said Saturday that Syrian President Bashar al-Assad must step down, but not necessarily immediately upon reaching a settlement to end the country's civil war.

Speaking after talks in London with British Foreign Secretary Philip Hammond, Kerry said he was prepared to negotiate to achieve a solution but asked whether Assad was.

Turkish fighter jets carried out a new barrage of cross-border airstrikes this week against Kurdish militants in northern Iraq, killing at least 55 rebels, state-run Anatolia news agency reported Saturday.

The strikes by F-16 and F-4 jets targeted caves, houses and camps used by the militant Kurdistan Workers Party (PKK), Anatolia said, citing unnamed security sources.

A five-year-old Syrian girl was found dead on Saturday and several other refugees were believed to be missing when their boat sank in an attempted crossing from Turkey to Greece, the state ANA agency reported.

The Greek coastguard rescued another 13 people and was looking for other survivors, the agency said.

Switzerland said Friday that it would take in 1,500 refugees and migrants over the next two years while strengthening support for Syria peace talks, which Bern called the "priority" for resolving Europe's humanitarian crisis. 

A Federal Council statement said Switzerland would only accept those "who have already been registered in Italy or Greece," the two countries which have received the overwhelming majority of people who have washed up on Europe's shores this year. 

The United States and Russia renewed high-level contacts between their militaries on Friday to discuss how to deal with the war in Syria.

U.S. Secretary of Defense Ash Carter and Russia's Defense Minister Sergei Shoigu spoke by telephone, spokesmen from their ministries said.

Syrian regime aircraft Friday carried out at least 25 strikes on jihadist-controlled Palmyra, the country's famed ancient city, with eight civilians among the dead, a monitoring group said.

The Syrian Observatory for Human Rights said the raids killed "at least eight civilians and many members" of the Islamic State jihadist group.