United Nations Secretary General Ban Ki-moon is in Russia, where he has said it is important not to "lose momentum" in talks on setting up a peace conference on Syria next month.
Mr. Ban is in the Black Sea resort town of Sochi to meet with Russian President Vladimir Putin for talks on Syria. Earlier Friday, he met with Foreign Minister Sergei Lavrov.
Russia has been pushing for inclusion of Syrian ally Iran and western ally Saudi Arabia in those talks, while accusing the United States of trying to narrow the field of participants.
Also Friday, the New York Times reported Friday that Russia has sent more advanced anti-ship cruise missiles to Syria. At the same time, Russia says it has no interest in seeing Mr. Assad remain in power.
On Thursday, U.S. President Barack Obama and Turkish Prime Minister Recep Tayyip Erdogan said they will keep pressure on Syria's president to step down.
Mr. Obama said at a joint White House news conference that he and Mr. Erdogan agree that President Bashar al-Assad should hand over power to a transitional body.