At least 15 people have been killed and 55 hurt in a bombing at a mosque in north Yemen, security sources say.
The blast occurred as Friday prayers ended at the Ben Salman mosque, often used by members of the security services, in Saada city.
Local officials have been cited as saying the bomb was hidden in a car or a motorcycle.
Abdulmalik al-Houthi, the leader of a Shia rebellion in the area, denied responsibility for the blast.
"We criticise and condemn this regrettable incident," he said in an interview with al-Jazeera television.
"We deny completely any role in this incident. It is not part of our ethics to target any mosque or any worshippers at all."
Hundreds of people have been killed in clashes in the region since a conflict between pro-government forces and rebels loyal to Mr Houthi broke out in 2004.
A BBC correspondent in Yemen says the mosque is often used by members of the security forces, which might have made it a target.
The region is a Shia stronghold, while most Yemenis are Sunni Muslims.
The Yemeni government says Mr al-Houthi's rebels want to overthrow it and impose Shia religious law. The rebels say they are defending their community against discrimination and what they call aggressive acts by the government.
Groups affiliated with al Qaeda have also staged attacks in Yemen.