Veteran Algerian diplomat Lakhdar Brahimi has agreed to replace Kofi Annan as the international mediator on Syria.
Mr Annan is stepping down at the end of August after six months in the job, after saying that his Syria peace plan was hampered by a divided and deadlocked UN Security Council.
Diplomats said Mr Brahimi had been undecided for days about whether to accept the offer of the post from UN Secretary-General Ban Ki-moon.
They said he did not want to be seen as a mere replacement of Mr Annan but wanted a reconfigured title and fresh approach to his mandate as a peace broker.
"He has agreed to take the post but with an amended title; he has new ideas about the approach to take," a UN source said on condition of anonymity, adding that Mr Ban accepted that.
Two Security Council diplomats confirmed the remarks.
UN officials said it was not clear when an official announcement would be made.
Mr Annan's title was joint special envoy for the United Nations and Arab League.
It remains unclear what Mr Brahimi's formal link with the Arab League, if any, will be, diplomats said.
They said Mr Brahimi would be based in New York, unlike Mr Annan, who is based in Geneva.
Syria had only accepted Mr Annan as a UN representative of the United Nations, not the Arab League, which suspended Syria's membership due to the escalating violence between forces loyal to Syrian President Bashar al-Assad and rebels determined to oust him.
Mr Brahimi, a veteran UN troubleshooter, has demanded "strong support" from the Security Council for efforts to secure a negotiated peace, envoys said.
End of observer mission
The UN Security Council confirmed it would not renew the mandate of the UN observer mission in Syria, which is due to expire in the coming days.
French UN Ambassador Gérard Araud said that the observers will begin to withdraw from the country.
Mr Araud, who is the president of the Security Council for August, said conditions for renewing the mandate had not been met.
Russian UN Ambassador Vitaly Churkin said the permanent five Security Council members and key regional players would meet on Syria in New York tomorrow.
He said he regretted that the UN observer mission will end.
Earlier, UN humanitarian chief Valerie Amos said as many as 2.5m people are in need of aid in Syria, because of the ongoing conflict between Syrian government forces and rebel fighters.
