US Secretary of State John Kerry is on his first official foreign trip with the Syrian conflict high on his agenda in Europe and the Middle East.
Mr Kerry is expected in London on Sunday. He will visit nine countries, including France, Turkey and Egypt.
In Berlin, he will meet Syrian opposition members and representatives of nations supporting them. He will also meet his Russian foreign minister Sergei Lavrov, at a time when relations between the United States and Russia are cool.
The US has sought Russia's backing to convince President Bashar al-Assad that he is isolated internationally.
Mr Kerry spent almost three decades as a member of the Senate Foreign Relations Committee.