Obama - on the final leg of his last trip to Europe as president of the US - and Merkel are expected to hold talks on Thursday followed by a news conference at which they will raise the issue of Syria, a source told the Reuters news agency.

The talks are scheduled for Thursday at 3:15 p.m. (1415 UTC) at the chancellory, while European leaders and Obama will meet on Friday to discuss extending sanctions against Russia for its intervention in Ukraine, and possible new sanctions for its bombing in Syria. The Kremlin has said it is maintaining a moratorium on air strikes in the city of Aleppo.

Obama has previously praised Merkel "a trusted partner" and supported her over the refugee crisis, while Merkel's congratulatory message to Trump following his victory in the November 8 election was somewhat perfunctory.

Key issues

Trump has signalled a possible rapprochement with Russia, raising doubts about the future of the sanctions regime introduced by Washington and Brussels in 2014 following Russia's intervention in Ukraine.

A German official told the DPA news service that the plan was to agree a rollover of EU sanctions against Russia, which are due to expire at the end of January, in the coming weeks.

European leaders will want clarity from Obama, who met Trump last week and said afterwards the president-elect would maintain core relationships around the world, including with NATO.

European officials fear that Russia will use the time before Trump's inauguration to launch new offensives in Syria and Ukraine. Two diplomatic sources said the issue of Syria would also come up at the Friday meeting.

jbh/bw (dpa, Reuters)