Thirteen protesters and two policemen were killed in violence in the capital Sanaa and Aden.
The deadliest clashes erupted in Sanaa as troops opened fire to break up protests, killing 12 people and wounding more than 130, medical sources said. Some of the victims were attacked with daggers, the sources said. Government officials said "tens of supporters of the government" were also wounded in Wednesday's clashes.
In the main southern city of Aden, two policemen and a protester were killed in a gunfight on Wednesday, a security official and medics said. Three protesters were also wounded.
In Riyadh, GCC's Assistant Secretary-General for Political Affairs Saad A. Alammar said the GCC General Secretariat is making all preparations for Sunday's high-profile political event.
Alammar, however, said the General Secretariat has so far not received the names of the leaders from Yemen’s six opposition groups who will sign the Gulf-brokered accord.
"On behalf of the United States, the signing ceremony will be witnessed by Gerald M. Feierstein, US ambassador to Yemen," said a spokesman for the US Embassy in Riyadh. Top officials representing the European Union and United Nations besides other regional and international organizations will also attend the event.
A GCC statement said the meeting would be chaired by Sheikh Abdullah bin Zayed Al-Nahyan, foreign minister of the UAE, which holds the current GCC presidency.
A joint meeting will later follow to formalize the GCC initiative, which calls for the creation of a national unity government and asks Saleh to transfer power to his vice president within 30 days after the agreement has been signed.
In exchange, Saleh and his family would receive immunity from prosecution.
The European Union urged all factions to finalize and implement the deal on Sunday.
In a statement sent to Arab News Wednesday, Catherine Ashton, the EU foreign policy chief, said: "I would like to thank the GCC for its hard work toward securing political agreement for transition in Yemen.
"I believe that the GCC initiative represents the best chance for Yemen to address the economic, social and security challenges ahead and to avoid escalation of violence."
