At least 22 people were killed on Saturday as Yemeni police opened fire on protesters and rival tribes clashed in Sanaa, while a suspected US air raid took out nine, including top Al-Qaeda leaders.
Police shot dead 12 people and injured dozens as they opened fire on demonstrators in Sanaa demanding President Ali Abdullah Saleh's resignation, medics said.
And barely two weeks after a drone killed US-born jihadist cleric Anwar al-Awlaqi, a suspected US air strike on Friday killed a raft of top Al-Qaeda leaders, including the media chief of Al-Qaeda in the Arabian Peninsula (AQAP), Egyptian Ibrahim al-Banna'a.
Banna'a was "in charge of the media arm of AQAP" -- the network's branch in Yemen -- and one of the group's "most dangerous operatives," the Yemeni defence ministry said, denying as in past such cases that the raid was American.
The son of Awlaqi, Abderrahman, 21, was also among the nine dead in the strikes that hit the militant-held town of Azzan in Shabwa, a member of Awlaqi's tribe said.
Also killed was Sarhan al-Qussa'a, brother of Fahd al-Qussa'a, a leader of AQAP, who was on a US wanted list, the Awlaqi tribesman said.
Sanaa routinely denies that the United States carries out raids on its territory, insisting Washington plays a purely logistic and intelligence role in support of Yemen's own counter-terror operations.
But last month, The Washington Post reported that the United States was building an array of secret new drone bases to strike Al-Qaeda targets in Yemen and Somalia.
On Monday, AQAP confirmed the death of Anwar al-Awlaqi in a US drone strike on September 30, and vowed revenge.
In Sanaa, security forces used live rounds as well as tear gas and water cannon to try to disperse hundreds of thousands of Saleh opponents trying to march on loyalist areas of the city centre from their Change Square stronghold, killing 12 people, witnesses and medics said.
"We demand from the Security Council to force Saleh to leave power," read a banner carried by protesters, as others carried a effigy of Saleh being hanged and posters of killed demonstrators, an AFP photographer reported.
The clashes erupted on Al-Zubeiri Street which marks the dividing line between parts of Sanaa held by troops loyal to Saleh and those held by dissident units under the command of General Ali Mohsen Al-Ahmar, who rallied to the opposition in March.
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Activists had called on protesters to march on the front lines on Saturday in a bid to bring to a head 10 months of increasingly bloody demonstrations against Saleh's 33-year rule in Sanaa.
State television said the "unauthorised" protest marched from Sitin Street to the area of Aser, which is under the control of Saleh loyalists, quoting claims from alleged witnesses that protesters opened fire at civilians.
An interior ministry official said that two members of the security forces were killed and 16 others wounded in clashes that accompanied the protest, according to Saba state news agency.
According to the unnamed official, five civilians were killed, including three children, and 10 others wounded in shelling of residential areas near the Al-Najda police base in Sanaa.
AFP was unable to verify the casualties through contacts with medics.
The official also claimed gunmen belonging to the tribal leader Sheikh Sadeq al-Ahmar, and soldiers from the dissident First Armoured Brigade, led by dissident General Ali Mohsen al-Ahmar were behind the attacks.
Also in northern Sanaa, 10 gunmen from the Hashid tribe which has sided with protesters against Saleh were killed in clashes with tribes loyal to the embattled president, a tribal source said.
The followers of tribal chief Sheikh Sadeq al-Ahmar were killed in shelling of their position near Al-Hassaba area, stronghold of the Ahmar clan, a source in the sheikh's office said.
Ahmar gunmen were locked on Saturday in fierce fighting with partisans of Sheikh Saghir bin Aziz, a tribal leader who has remained loyal to Saleh.
In an apparent revenge attack after the raid on Al-Qaeda chiefs, saboteurs launched a rocket-propelled grenade assault on a pipeline serving the Shabwa gas terminal of Balhaf, halting exports, an engineer at the facility said.
The saboteurs struck in Al-Hadhina, two kilometres (a little over a mile) from the Balhaf terminal on the Gulf of Aden, another Shabwa provincial official said, asking not to be identified.
The veteran president has refused to step down despite increasingly strident calls for his departure from both Western governments and impoverished Yemen's wealthy Arab neighbours in the Gulf.
According to a letter from Yemen's youth movement sent to the United Nations earlier this month, at least 861 people have been killed and 25,000 wounded since mass protests erupted across the country.