Yemen's ruling party and the opposition traded accusations for their failure to sign a Gulf-brokered power-transition deal after Gulf Cooperation Council (GCC) mediator Abdulatif al-Zayani left Sanaa Wednesday evening.

GCC Scretary-General al-Zayani, who spent five days?Sanaa trying to get the deal signed, left shortly after he told Yemeni President Ali Abdullah Saleh that the opposition Joint Meeting Parties had accepted all his conditions and it was his turn to sign the agreement.

Saleh, who had refused to sign the deal on April 30, however, responded by putting more conditions on the deal, which tired the GCC mediator out.

Al-Zayani did not publicly comment on the matter, but the Yemeni rivals blamed each other for jeopardizing the Western-backed deal on a peaceful transition of power in Yemen.

"Al-Zayani left after the opposition's representatives refused to meet their rival's demand, namely talking about the arrangements after both sides ink the GCC deal," an official from the presidential palace told Xinhua on condition of anonymity.

Another government official said al-Zayani left as the opposition refused to replace its representative Mohamed Basundowa with the opposition rotating chairman Yaseen Saieed Noman as Saleh required.

"Because Saleh said Basundowa did not represent the opposition," the official said.

Meanwhile, the opposition spokesman Mohamed Qahtan refused to comment on the issue, but said, "We (the opposition) have agreed on everything and we informed al-Zayani our readiness ... We are waiting for Saleh to sign the deal first, so we will then sign it too."

Earlier in the day, an official from the presidential palace told Xinhua that Saleh and his ruling party agreed to sign the GCC deal on Wednesday and the signing ceremony might be held in the next few hours.

Under the deal, pressed by Western countries and Gulf mediators, Saleh would leave office within 30 days after signing the deal in exchange for immunity from prosecution, and a new government, to be formed by the opposition within seven days, should arrange the presidential and parliamentary elections in 60 days.

Failure to sign the deal would further escalate the military tensions between Saleh's forces and the defected army, according to local observers.

The United States expressed its concern about the growing violence in the country.

A White House official on Wednesday urged Saleh to sign and implement the GCC-brokered deal for the country to "move forward immediately with its political transition."

After a phone conversation with Saleh, John Brennan, U.S. President Barack Obama's top advisor on homeland security and counterterrorism, said the transfer of power "represents the best path forward for Yemen to become a more secure, unified and prosperous nation and for the Yemeni people to realize their aspirations for peace and political reform."

Yemen also witnessed mass anti-government protests of civil disobedience in major provinces on Wednesday. Several deadly clashes with government forces were reported.