Germany’s top diplomat will host talks on Wednesday with his French counterpart, the UN’s Syria envoy and Syria’s main opposition leader.

Germany's top diplomat will host talks on Wednesday with his French counterpart, the UN's Syria envoy and Syria's main opposition leader, as concerns grow over the war-torn country's faltering truce.

Discussions will focus on "how the conditions for a continuation of the peace talks in Geneva can be met, as well as how a reduction of violence and an improvement in the humanitarian situation in Syria can be achieved", the German foreign ministry said in a statement on Tuesday.

The Berlin meeting comes in a week of whirlwind diplomacy seeking to salvage a ceasefire in Syria, with US Secretary of State John Kerry jetting into Geneva last Sunday for talks with UN envoy Staffan de Mistura.

The UN envoy was himself in Moscow for talks with Russian Foreign Minister Sergei Lavrov on Tuesday, before heading to Berlin to meet with host Frank-Walter Steinmeier, France's Foreign Minister Jean-Marc Ayrault and Syrian opposition leader Riad Hijab.

A two-month-old ceasefire brokered by Washington and Moscow is hanging by a thread as fierce fighting has again erupted around Syria's second city Aleppo.

The clashes have also threatened peace negotiations, which de Mistura had hoped could resume next month.