By Mohamed Sudam and Mohammed Ghobari
SANAA (Reuters) - Yemen's ambassador to the United Nations Abdullah Alsaidi resigned his post on Sunday as defections picked up steam after snipers firing from rooftops shot dead up to 52 anti-government protesters on Friday.
In Sanaa, mourners started burying the dead in side-by-side graves in a small cemetery near a military camp in the Arabian Peninsula state, where tens of thousands of people have protested for weeks against President Ali Abdullah Saleh's 32-year rule.
But the police, who protesters blame for the deaths, withdrew from public sight near protest areas to be replaced by soldiers dressed in camouflage uniforms but bearing only batons, in an apparent bid to reduce tensions.
"This is an acknowledgment of the failure of the security in repressing the revolution, and the crowds that came out today are a signal of the readiness to put forth more sacrifices," opposition spokesman Mohammed al-Sabry said.
Friday's bloodshed prompted Saleh, struggling to preserve his rule, to declare a state of emergency for 30 days that restricts freedom of movement and the right to gather. It also grants police more leeway to make inspections and arrests.
A government source said neighboring Saudi Arabia, the world's top oil exporter, had been trying to quietly mediate even before Friday's shooting, and efforts were continuing.
Tanks stood guard near the presidential palace in Sanaa and armored vehicles were positioned outside sensitive locations.
But tension in the capital appeared lower, and ambulances ferried the bodies, draped in Yemeni flags, to the cemetery. In the protest camp near Sanaa University, mourners placed roses at a site where five protesters died.
"We have one aim, but revolutions require sacrifices, and we are willing to give more of our blood for our cause," said Wassim al-Qudsi, a young man who was among the mourners.
Saleh, also trying to cement a northern truce and quell southern separatism, has rejected demands to resign immediately, promising instead to step down in 2013 and offering a new constitution giving more powers to parliament.
Doctors said the death toll from the shooting rose to 52, higher than the 25 deaths confirmed by the interior ministry.
Protesters said they had caught at least seven snipers carrying government identity cards who they said had been involved in the shooting, but Saleh denied this, blaming gunmen among the protesters for the violence.
A string of his allies have since broken ranks to join protesters frustrated by rampant corruption and soaring unemployment. Some 40 percent of the population live on $2 a day or less in Yemen, and a third face chronic hunger.
In addition to the U.N. envoy, Yemen's Minister for Human Rights Houda al-Ban also resigned her post on Sunday, making her the second cabinet member to defect since Friday.
"The critical situation prevents us from continuing in our jobs under a regime that does not respect human rights and freedoms," Ban said, speaking also on behalf of her deputy Ali Tayseer.
Tourism Minister Nabil Hasan al-Faqih resigned and quit the ruling party on Friday. The head of the party's foreign affairs committee also left, as did a former ambassador to Russia.
Since then, two other prominent members of Yemen's ruling party also quit including the head of the state news agency, Nasr Taha Mustafa. A former ambassador, Abdul Malek al-Iryani, also declined an invitation to join the country's Shura Council.
Washington, which sees Yemen as a key ally against a resurgent al-Qaeda wing, said U.S. citizens should avoid areas of planned demonstrations, which could turn violent. It has already urged Americans to leave Yemen.
As unrest continued across Yemen, tribesmen fired rocket-propelled grenades at a power plant in Maarib province on Sunday, cutting electricity to parts of the capital and the southern port city of Aden, a government source said.
(Additional reporting by Cynthia Johnston in Sanaa, Editing by Jon Boyle)