U.N. Secretary-General Ban Ki-moon says "enough is enough" in Syria, calling the civil war there a breeding ground for extremists and terrorists.
Mr. Ban spoke Wednesday on the first day of Syrian peace talks in Montreux, Switzerland. The United States and Russia are sponsoring the meeting. More than 40 delegations are attending.
The U.N. chief says he did not expect any instant breakthroughs, and that everyone understands the talks will be difficult. But he said the Syrian people are "desperately looking for relief from the nightmare in which they are trapped."
The U.N. says the goal of the talks is setting up a transitional government in Syria.
U.S. Secretary of State John Kerry says there is no way Syrian President Bashar al-Assad can stay in power, calling him a magnet of terrorism.
Opposition leader Ahmad Jarba accused Mr. Assad of Nazi-style war crimes.
Syrian Foreign Minister Walia al-Moallem insisted that President Assad is staying. He bitterly accused the West of backing terrorists -- the Syrian government's word for the opposition.
Moallem refused to give up the podium, despite Mr. Ban's insistence that he refrain from inflammatory statements. Moallem angrily told the U.N. chief, "You live in New York. I live in Syria, I have the right to give the Syrian version here in this forum. After three years of suffering, this is my right.''
U.N. mediator Lakhdar Brahimi says he will meet Syrian opposition and government delegations separately on Thursday, hoping he can arrange a face-to-face meeting when the talks resume Friday in Geneva.
Brahimi said he has "fairly clear indications" that the parties are ready to discuss prisoner swaps, humanitarian access and local cease-fires.
Iran, Syria's top regional ally, was notably absent from the talks. Iran was uninvited when it rejected a possible transitional government for Syria. Iranian President Hassan Rouhani said Tehran's exclusion means the talks are likely to fail.