Special envoy Kofi Annan warned of an "escalation" of the Syria conflict into the rest of the Middle East unless it is carefully handled as he called on the UN Security Council to unite to put pressure on President Bashar al-Assad.
Mr Annan gave his warning as Turkey told its nationals to leave Syria where thousands took part in new protests against the government.
Activists said at least another 15 people were killed.
The UN-Arab League envoy has ordered a team of UN experts to Damascus this weekend to discuss a possible ceasefire and international monitoring mission, his spokesman said.
All countries around Syria are worried about fallout from the uprising, Mr Annan told reporters after briefing a closed session of the UN Security Council on the crisis.
"We tend to focus on Syria, but any miscalculation that leads to major escalation will have impact in the region which would be extremely difficult to manage," he told reporters in Geneva, according to an official transcript.
"The region is extremely concerned about developments in Syria. Their concern goes beyond Syria itself because the crisis can have a serious impact for the whole region if it is not handled effectively."
Turkey strongly urged thousands of nationals to leave Syria because of the "serious security risks" and said it was considering withdrawing its ambassador from Damascus.
Mr Annan told the Security Council he has had a "disappointing" response from Mr Assad so far to his proposals, diplomats at the meeting said.
He appealed to the badly divided council to get behind his mission in a bid to sway Mr Assad.
"The stronger and more unified your message, the better chance we have of shifting the dynamics of the conflict," Mr Annan was quoted as telling the 15-nation council.
The UN says some 8,000 people have died since opposition protests flared last March. Activists have given a toll of 9,100.
But the Security Council has been unable to pass a resolution condemning the violence. Russia and China have twice used their powers as permanent members to block resolutions which they said were unbalanced.
