Veteran Algerian diplomat al-Akhdar al-Ibrahimi takes up the mission aimed at ending the ongoing crisis in Syria.
Ibrahimi who made his name brokering an accord in Lebanon's civil war in the 1980s and as a UN envoy to Afghanistan and Iraq, was to hold meetings Saturday at the UN headquarters ahead of a handover encounter on Tuesday with UN leader Ban Ki-moon and Annan, a UN spokesman said.
Ban and Ibrahimi will discuss the crisis at the UN General Assembly the same day.
He expects to go soon to Damascus to meet Assad and to Cairo for talks with Arab League officials, said his spokesman Ahmad Fawzi. But no details of any initiative have yet emerged.
Annan halted his six month battle to make Syrian government and insurgents lay down their guns, complaining at the lack of international support for his six-point peace plan.
The international powers also signed up for an accord agreed at a Geneva meeting with Annan on June 30 which called for a transitional government.
However, Ibrahimi has made no firm commitment to keep to them.
"I have a tool box and there are several useful tools that are in that tool box that I can use when and if possible," Ibrahimi's spokesman quoted him as saying.