The veteran Algerian diplomat Lakhdar Brahimi has replaced Kofi Annan as international mediator on Syria, as the 17-month conflict slides deeper into civil war.
Mr Brahimi, who served as a UN envoy in Afghanistan and Iraq, formally accepted the post and will resume efforts for a diplomatic solution to Syria's crisis, said Eduardo del Buey, the deputy spokesman for the UN secretary general, Ban Ki-moon.
"The violence and the suffering in Syria must come to an end," Mr del Buey said.
"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."
The announcement came as the situation in Syria - and its spillover - showed no signs of abating.
At least 72 people were killed across the country as the regime continued its onslaught, according to the Syrian Observatory for Human Rights, a watchdog with a network of activists on the ground.
For the first time the government acknowledged, through state media, that it was fighting rebels near the airport in Aleppo, the country's largest city.
Meanwhile, a second Turkish citizen has been kidnapped in Lebanon, Ankara announced, warning its nationals against travelling to the country.
Members of a Lebanese Shiite clan kidnapped more than 20 people on Wednesday, including a Turkish businessman, in retaliation for the capture of one of their kinsmen in Syria.
The UAE and other Arabian Gulf states told their citizens to leave Lebanon after Wednesday's kidnappings and threats to seize more citizens of countries that have backed the uprising against Bashar Al Assad, the Syrian president.
It was not immediately clear if Thursday's kidnapping was related to the earlier abductions.
The US sent out a similar travel warning yesterday, saying its nationals face increased threats to their security in Lebanon, including the possibility of targeted kidnappings or terrorist attacks.
Mr Brahimi was expected to arrive in New York next week to meet Mr Ban and discuss plans for a fresh approach to the Syria conflict, which the United Nations says has killed more than 18,000 people.
Mr Brahimi, 78, who emerged last week as the leading candidate to replace Mr Annan, brings a long record of working in the Arab and Islamic world. He served as Algeria's foreign minister from 1991-93 and joined the UN in 1994, where he served in a variety of high-profile posts until he retired in 2005.
Mr Annan said this month that he would resign on August 31 as joint UN-Arab League envoy to Syria, after failing to broker a ceasefire as the country descended into civil war.
As an Arab League envoy, Mr Brahimi helped negotiate the end of Lebanon's civil war.
Expectations for what Mr Brahimi can accomplish should be lower than they were for Mr Annan, whose mission suffered from unrealistic hopes, said Richard Gowan, the associate director of the New York University Center on International Cooperation. Still, Mr Brahimi is the right kind of negotiator for the job, he said.
"Brahimi has an incredibly strong reputation around the UN, but is also well-known for not taking orders from the big powers or worrying too much about media attention," Mr Gowan said. "This may be just what is needed in Syria now: a hardened but independent mediator, who will stick with diplomatic efforts even if he faces a lot of criticism for failing to cut a deal fast."
* Associated Press with additional reporting by Reuters and Agence France-Presse