At least 42 people have been killed in 10 days of clashes in Yemen between Sunni Islamists and Shiite rebels, tribal sources and an official said on Monday.
Tension is mounting with stumbling national reconciliation talks, begun after the ouster of former president Ali Abdullah Saleh last year, set to conclude this month.
There have been days of clashes between gunmen loyal to tribal chief Hamid al-Ahmar -- a leader of the Sunni Islah party, and Shiite Huthi rebels in Amran province north of the capital, several sources said.
More than 30 people have been killed in the past 10 days in fighting in Osaymat and Ozur, a tribal chief said of two areas named after the Sunni and Shiite tribes who live there.
At least 12 others were killed in firefights between Huthis and Sunni Islamists in the Rudma region near Ibb, a local official said.
The Huthis' Ansaruallah website accused Ahmar and his Islah party of sending scores of gunmen to Amran and Ibb.
Meanwhile, two bombs exploded on Monday in Sanaa.
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They targeted two buses carrying members of the air force and the military academy, a security official was quoted by the official Saba news agency as saying.
One bomb exploded on Airport Road and the other on Al-Nasr Street in eastern Sanaa, the official said.
He said the explosions caused only minor damage, and did not say who was suspected of carrying out the attacks.
Last month, a bomb planted on an air force bus killed one person and wounded 25 when it exploded on the road to Sanaa's international airport.
The Yemen-based Al-Qaeda in the Arabian Peninsula (AQAP), the most active franchise of the global jihadist network, has staged many attacks on the country's security forces.
However, the rising unrest is also seen as an attempt to derail an already shaky national reconciliation dialogue aimed at drafting a constitution and preparing for elections in February 2014.
"These are attempts to destabilise Yemen and push the national dialogue to failure," said Mohammed al-Moqbeli, a representative of Yemeni youth in the talks.
Southern separatists on Monday returned to the talks after staging a walkout last month over various demands, including that the talks be held abroad.