At least six people died as gun battles broke out Monday between Yemeni President Ali Abdullah Saleh's security forces and members of a key tribe aligned with the opposition.
The clashes happened in the capital, Sana'a, near the house of tribal leader Sheik Sadeq al-Ahmar. Al-Ahmar in March joined the opposition movement that is demanding Mr. Saleh's immediate resignation. At least 25 others were wounded in Monday's clashes.
The clashes come amid international pressure on Mr. Saleh to provide a peaceful transition ending his more than three decades of autocratic rule.
A council of Arab states suspended its mediation efforts on Sunday after Mr. Saleh refused to sign a deal for him to leave office.
The Gulf Cooperation Council made the decision when Mr. Saleh backed out of the deal after Yemen's opposition signed the pact on Saturday with the understanding that the president would sign it on Sunday.
It was the third time the Yemeni leader has refused to sign the deal.
U.S. State Department spokesman Mark Toner said Monday the United States believes Mr. Saleh can still sign the agreement to break the political "deadlock" that has plagued the Arab country and "urged him to take action."
The agreement offered Mr. Saleh immunity from prosecution if he transfers power to a deputy within 30 days of signing.
U.S. Secretary of State Hillary Clinton says the United States is "deeply disappointed" by Mr. Saleh's refusal to sign the deal. In a statement late Sunday, she also said Mr. Saleh is turning his back on his commitments and disregarding the aspirations of the Yemeni people.`
In a speech Saturday, the president denounced the U.S.-backed proposal as a "coup" and warned that his departure could allow al-Qaida to take over parts of Yemen.
Some information for this report was provided by AP and AFP.