New UN-Arab League envoy Lakhdar Brahimi said that he was "scared" at the size of the task of ending the Syria conflict.
The former Algerian foreign minister spoke as he started meetings with UN Secretary-General Ban Ki-moon, UN ambassadors and other top officials before replacing Kofi Annan on September 1.
"When you called me, I told you that I was honored, flattered, humbled and scared. I am still in that frame of mind," Brahimi told Ban before their meeting at UN headquarters.
"I will definitely give this my very, very best. I know a few people in Syria and in the region," added Brahimi, who as an Arab League envoy brokered the 1989 accord that ended Lebanon's civil war.
Ban said that the new envoy faced a "crucial task" as the Syrian war worsens. The UN leader made a new plea for the divided UN Security Council to unite behind Brahimi.
The Algerian diplomat has already been criticized by some Syrian opposition groups for not calling for President Bashar al-Assad to step down.
Brahimi said, however, that the Syrian people "will be our first masters."
"We will consider their interests above and before anyone else. We will try to help as much as we can, we will not spare any effort," he added.
Annan, a former UN chief, ended his six-month bid to bring peace to Syria, complaining about the lack of international support for his efforts to make Assad implement an agreed peace plan.
As the war grows increasingly bloody, Brahimi has indicated that he will try new tactics. He is due to spend a week in New York holding talks with UN political, humanitarian and other officials and diplomats to set up his mission, officials said.
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"That peace plan remains intact," said UN spokesman Martin Nesirky, who added that Annan's plan and the Geneva accord calling for a political transition in Syria, are "building blocks for Mr Brahimi to use."
"Of course, he will be looking with other UN officials at how this is going to be taken forward. But at this point, we can't really comment on what that might be," Nesirky told reporters.
Ban, "deeply concerned" about the spiraling violence, said that Brahimi was taking on "a very important, crucial task, to bring peace and stability and the promotion of human rights in Syria."
He called Brahimi an internationally respected statesman of "extraordinary talent and experience in the region."
"The longer this fighting goes on, the more people will be killed, the more people will suffer," Ban said.
"It is crucially important that the Security Council, the whole United Nations System is supporting your work."
Later, Brahimi met with France's UN envoy Gerard Araud to discuss "the challenges of his mission and the situation in Syria," French diplomats said.
The pair "agreed to hold an informal meeting with Security Council members which will take place soon," they said.
The five permanent members of the Security Council are seriously split over Syria. Russia and China have blocked three resolutions on the conflict that could have led to sanctions against Assad. They in turn have accused western nations of only seeking regime change.
With Syrian activists now putting the toll from the 17-month-old conflict at more than 24,500, the first test of international unity will be at a UN Security Council ministerial meeting on August 30 on the humanitarian impact of the civil war.
French Foreign Minister Laurent Fabius is scheduled to chair the meeting as France is Security Council president for the month of August. It is not yet clear which other ministers will attend.