Government airstrikes in southern Yemen targeting al Qaeda linked militants accidentally killed 40 pro-government tribesmen, a Yemeni security official and a tribal chief said.
The botched airstrikes reflect the deteriorating security situation that has spread across the impoverished, heavily armed country since the popular uprising against longtime President Ali Abdullah Saleh began six months ago.
Armed tribesmen are battling government forces in a number of areas around the country, and Islamist militants, some linked to al Qaeda, have overrun entire towns in the country's restive south and are now fighting government forces and tribes that remain loyal to Saleh.
The president has clung to power despite the months of protests and being seriously wounded in an attack on his palace compound in the capital, Sanaa, on June 3. His wounds forced him to travel to Saudi Arabia for medical treatment, and he has yet to return. But Saleh has maintained his power through his son, who controls some of the country's best trained military forces.
The movement seeking an end to the president's 33 years in power got a boost on Saturday with the announcement of a new tribal alliance whose leaders are pledging to defend the uprising.
Yemen's Tribal Alliance will group together one of the most powerful tribal confederations, the Hashid, and a number of tribes from the country's largest tribal confederation, the Bakil.
The Hashid leader already turned against Saleh in March, and fighters under his command have battled loyalist troops in the capital and elsewhere.