International mediator Lakhdar Brahimi said after talks with President Bashar al-Assad that the escalating Syrian conflict poses a global danger.
"We discussed the Syrian crisis and I repeat, this crisis is very dangerous," Mr Brahimi told reporters after he met Mr Assad for an hour at the presidential palace.
"This crisis is deteriorating and represents a danger to the Syrian people, to the region, and to the whole world."
Activists say more than 27,000 people have been killed in the 18-month-old conflict between Mr Assad's forces and the mainly Sunni Muslim rebels determined to overthrow him.
Today’s meeting in Damascus was Mr Brahimi's first with Mr Assad since he replaced Kofi Annan as United Nations and Arab League peace envoy two weeks ago.
The veteran Algerian diplomat described the mission as "nearly impossible".
Mr Assad's forces and the outgunned but increasingly powerful rebels seeking his overthrow have ignored appeals to end the fighting, which has continued in most of the country's main cities, including Damascus, Aleppo, Homs and Deir al-Zor.
Damascus residents reported hearing heavy overnight bombardment followed by the sound of jet planes swooping over the capital shortly after 7am (5am Irish time) today.
The Syrian Observatory for Human Rights, a British-based group monitoring the violence, said 160 people were killed in Syria yesterday, as Mr Brahimi met Russian and Chinese diplomats in Damascus. On Thursday he spoke with the Iranian ambassador.
Russia, Iran and China are supporting Mr Assad's government and Moscow and Beijing have three times blocked Western-backed attempts in the UN Security Council to criticise and threaten sanctions against Damascus.
"I believe that the president realises more than me the dimensions and the danger of this crisis," Mr Brahimi said.
Mr Brahimi said Mr Assad and his officials had pledged to support his work, adding that he would return to the region soon after talks in New York with United Nations Secretary-General Ban Ki-moon.
Syria's UN envoy Bashar Ja'afari said earlier this month Damascus was "open-minded and fully committed to the mission of Mr Brahimi in his endeavours to put an end to violence and find a Syrian-led political solution to the crisis".
