'We can't beat Isis with military means': Germany

"We stand before the dilemma that the battle against Isis must be continued, but everyone also knows that in the end the battle against terrorism can't be won militarily," Steinmeier told journalists as he arrived at an EU foreign ministers' meeting in Brussels.

"I personally remain convinced that... we will only move forward in the Middle East if, above all, we work energetically on those questions which can lead to a de-escalation of the conflict in Syria," he said.

Steinmeier praised the Vienna talks which have managed to bring together not just world powers including Europe, the USA, Russia and China, but also regional powers "from Turkey, to Saudi Arabia, to Iran".

The talks had already achieved a momentum that would make it difficult for any party to withdraw, he said.

Under agreements reached at two summits on Syria in recent weeks, there is now a timetable for talks between the Syrian government and opposition groups and a temporary government to oversee new elections with United Nations oversight within 18 months.

But Steinmeier also noted that alongside the "core conflict" between President Bashar al-Assad and rebels, the fight against Isis would have to go on.

He said that Germany was already doing a lot by arming and training Kurdish Peshmerga fighters who in recent days have taken back territory from Isis.

"We will have to do both, we will continue our support in the fight against Isis, but we will also have to search even harder to solutions for the core conflict, the civil war in Syria, now in its fifth year," he said.