Former Algerian foreign minister Lakhdar Brahimi will replace Kofi Annan as the international envoy working to bring an end to the conflict in Syria, the UN has announced.
Mr Annan ended his attempts to bring peace to the country, which has seen an estimated 21,000 people killed during a 17-month uprising, after it became clear his six-point plan was being ignored by both sides.
Violence has soared in recent months as the rebel Free Syrian Army has gained in strength, launching attacks on regime forces in Damascus and Aleppo, Syria's largest city.
Sky News' foreign affairs editor Tim Marshall said there was heavy fighting in the capital overnight as opposition forces attempted to shoot down military helicopters over the city.
Later, clashes took place around the main military airport and the army shelled a neighbourhood in south Damascus. Opposition activists claimed 65 bodies had been found dumped on a rubbish tip in a town outside the capital.
Deadly violence was also reported in Aleppo, Homs and Deraa.
Mr Brahimi, previously a UN special envoy in both Iraq and Afghanistan, was named as Mr Annan's successor just hours after the mandate of the UN observer mission tasked to monitor the ceasefire elements of his plan ended.
He is expected to travel to New York in the coming days to meet UN Secretary General Ban Ki-moon to discuss a fresh approach to the conflict.
In a statement, Mr Ban said: "The violence and the suffering in Syria must come to an end.
"The Secretary General appreciates Mr Brahimi's willingness to bring his considerable talents and experience to this crucial task for which he will need, and rightly expects, the strong, clear and unified support of the international community, including the Security Council."
However, the United States was quick to question how Mr Brahimi would operate following the withdrawal of the UN monitors.
White House deputy press secretary Josh Earnest said: "We need to hear more from the UN on the mandate of Mr Brahimi's new position."
Turkey's foreign minister cautioned that international consensus would be needed if the new envoy was to succeed.
When he resigned, Mr Annan complained that his efforts were hampered by a divided and deadlocked UN Security Council.
Meanwhile, it has emerged Syria's first astronaut has joined the ranks of prominent defectors from the regime.
General Muhammed Ahmed Faris, a military aviator and the first Syrian in space when he flew with a Soviet crew to the Mir space station in 1987, fled to Turkey 10 days ago.
"I decided to defect from the regime several months ago, but I was kept under surveillance and it prevented me from defecting immediately," he told Reuters news agency.
He said seeing an eight-month-old child wounded by shrapnel was the final straw for him.
