US secretary of state Hillary Clinton is accusing Yemen's president of turning his back on his commitments after he rejected a deal to step down.
Clinton urged Ali Abdullah Saleh on Monday to sign the US-backed agreement in order to prevent further chaos that has consumed Yemen for the past three months.
"We urge him to immediately follow through on his repeated commitments to peacefully and orderly transfer power and ensure the legitimate will of the Yemeni people is addressed. The time for action is now," Clinton said in a statement.
Despite intense diplomatic pressure from Yemen's Gulf Arab neighbours and Western mediators, Saleh rejected the deal that would have given him immunity from prosecution.
The mediators were hoping to bring an end violence in which more than 170 Yemeni demonstrators have been killed.
"The United States is deeply disappointed by president Saleh's continued refusal to sign the Gulf Co-operation Council initiative," Clinton said.
It was the third time an agreement for him to leave after 33 years in power had fallen through at the last minute.
"President Saleh is now the only party that refuses to match actions to words," Clinton said, adding that the other parties to an agreement already had signed off on it several times.
|Click here for more of Al Jazeera's special coverage
Saleh refused twice before to sign the agreement. But this weekend it had appeared he was finally relenting, under intense pressure from his allies, the United States and Gulf Arab countries that mediated the accord.
The opposition parties signed the accord on Saturday, and the Yemeni president grudgingly promised he would sign the following day.
Instead, the defiant leader showed his determination to cling to the power he has held for 32 years, despite increasing isolation.
His regime unleashed hundreds of armed loyalists into the streets of Sanaa on Sunday in an apparently orchestrated campaign to demand he not step down.
Saleh supporters, armed with guns, knives and swords, trapped US, European and Arab ambassadors at the diplomatic mission of the United Arab Emirates (UAE) in Sanaa.
The diplomats had gathered at the embassy, waiting to be taken to the presidential palace for the expected signing at noon.
Security forces broke up the crowd after several hours of letting them besiege the embassy on Sunday. Clinton said the US was outraged about the incident.
"We condemn this action and call on President Saleh to meet his international obligations to ensure the safety and security of all foreign diplomats and their staffs working in Yemen."
The diplomats were reported to have left by helicopter, after the UAE urged Yemeni authorities to secure its embassy.
Yemeni state TV later showed several top figures from Saleh's ruling party signing the accord as the president and Gerald M. Feierstein, the American ambassador, watched. But Saleh himself refused.
Saleh said afterward he would not do so unless opposition leaders come to the palace and sign it as well in public, not "behind closed doors".
"If they don't comply, they are dragging us to a civil war, and they will have to hold responsibility for the bloodshed in the past and the blood which will be spilled later on because of their stupidity," Saleh warned in an address on state TV.
The opposition appeared to dismiss Saleh's demands that they participate in a public signing.
Yemeni opposition official Abdul-Malak al-Mukhlafi said the mediators from the Gulf Cooperation Council - a grouping of six Gulf Arab nations - had set down in a three-page document the details of how the deal was to have been signed and that any change in that process was considered a breach of the agreement.
"This regime is taking the world and its people lightly," he told The Associated Press news agency.
"We ask the international and regional community to pressure the regime and force it to respect the will of the people, and to impose sanctions that will make it respond to the people's demands."
In Riyadh, the Saudi capital, five foreign ministers from the Gulf council held an emergency meeting on Sunday to discuss what happened.
A Saudi diplomat said there is "anger" over Saleh's position. He spoke on condition of anonymity because he was not authorised to talk to the media.
The ministers decided to suspend the initiative "because conditions were not ripe," according to a statement from the meeting. Still, they urged Saleh to sign in the "soonest possible time," he said.