Members of the UN Security Council also failed to come up with a joint statement on Yemen after adding the country's presidential crisis to their agenda for the first time.
The organising committee of youth protests called in a statement for "marches in millions" across the country in protest at the killing of protesters on Tuesday, and to stress rejection of any deal that does not include the immediate departure of embattled President Ali Abdullah Saleh.
Confrontations between security forces and protesters demanding the ouster of Saleh raged on, with medics and witnesses reporting eight people, including a passer-by and a policeman, shot dead.
One protester was killed when a gunman on a motorbike opened fire at dawn on Wednesday at demonstrators staging a sit-in at Al-Nasr Square in the western Red Sea city of Hudaydah.
The assailant managed to escape after also wounding some eight other protesters, most of whom were asleep.
Also Wednesday, a policeman was shot dead Wednesday in clashes between police and protesters in the southern city of Aden, while five protesters were shot dead in Sanaa on Tuesday.
Foreign ministers of the Gulf Cooperation Council held talks on Tuesday with representatives of Saleh as part of efforts to hammer out a deal by which Saleh would step down.
But the meeting in Abu Dhabi appeared to have made no major progress as a curt, vague statement issued after the meeting described the talks as "constructive," vowing to "exert more effort to preserve security, stability and the unity of the Yemeni state."
"During the meeting both sides exchanged opinions over the Gulf initiative," the statement said.
The spokesman of the Yemeni delegation, Ahmed bin Dagher told reporters after the meeting that any solution should not clash with the constitution.
"We adhere to the constitution which we cannot breach," he said, in a statement that could mean that Saleh should serve out his term until 2013 -- a position stated previously by the ruling General People's Congress party.
He told Al-Arabiya television that "no immediate solution has come out of the meeting."
The meeting followed talks held on Sunday in Riyadh between the Gulf ministers and representatives of the parliamentary opposition, who are adamant that Saleh should step down immediately, after being in office since 1978.
Saleh has since January faced protests calling for his departure, in which over 130 people have been killed.
On April 10 the GCC -- Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates -- appealed to Saleh to "announce the transfer of his powers to the vice president," Abdrabuh Mansur Hadi.
It also called for the formation in Yemen of "a government of national unity led by the opposition" which would be responsible for "establishing a constitution and organising elections."
The opposition objected to the wording of the proposal, insisting on Saleh stepping down completely and not just handing over authority to his deputy.
Last week, Saleh's office said in response to the GCC mediation bid that the president has "no reservation about transferring power peacefully and smoothly within the framework of the constitution".
Saleh has so far insisted on overseeing any transition, fearful of being hounded out of office and faced with prosecution like his ally, Egypt's former president Hosni Mubarak, who resigned on February 11 following mass protests.
Meanwhile, a press statement on Yemen drawn up by Germany and Lebanon, two of the members on the 15-nation UN Security Council, was blocked by a minority of nations during the Tuesday meeting, diplomats said.
German envoy Peter Wittig said, however, that discussing Yemen in the council "sends an important signal by the international community: the negotiations should not stall and further bloodshed has to be avoided."