About 18 people were killed and more than 45 wounded today when a bomb hidden in a motorcycle exploded outside a mosque in Yemen's volatile northern city of Saada where army officers were praying.
A security source said several suspects had been detained at a checkpoint in Saada and preliminary investigations showed rebels loyal to Abdul-Malik al-Houthi were behind the attack.
The northern province has been rocked by sporadic violence since a conflict broke out in 2004 between government forces and Houthi, a member of the Zaydi sect of Shi'ite Islam.
Houthi denied any role in the blast that took place as worshippers left the Salman Mosque after Friday prayers.
"We criticise and condemn this regrettable incident ... We deny completely any role in this incident. It is not part of our ethics to target any mosque or any worshippers at all," he told Al Jazeera television by telephone from Saada.
"We believe that someone is trying to blow up a war and foil all the peace efforts through these incidents ... The real target of these incidents is us, the people of Saada."
Yemen has witnessed attacks by different groups targeting everything from tourists and embassies to government offices and oil pipelines in recent years, but attacks on mosques were virtually unheard of until Friday.
Sunni Muslims form a majority of Yemen's 19 million population, while most of the rest, including Houthi's supporters are Zaydis. It is not unusual for members of both communities to pray together.
The mosque preacher, Askar Zaayl, who is also an aide to Ali Mohsen, Yemen's northern military commander, told Al Jazeera he was among those targeted in the attack and pointed the finger at "the militias led by Abdul-Malik al-Houthi."