(Recasts, adds Interior Ministry official paragraph 11, edits)

By Mohammed Sudam

SANAA, May 2 (Reuters) - About 15 people were killed and dozens wounded on Friday in the bombing of a mosque in Yemen's volatile northern city of Saada that officials blamed on followers of rebel leader Abdul-Malik al-Houthi.

A conflict in Saada broke out in 2004 between the government and Houthi, a member of the Zaydi sect of Shi'ite Islam, and violence has flared in recent weeks after a period of calm.

A security source said several suspects had been detained at a city checkpoint and preliminary investigations showed Houthi's followers planted the bomb, which was hidden in a motorcycle parked outside the Bin Salman Mosque.

Houthi denied any role in the blast, which took place as worshippers, including army officers, left the mosque.

"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."

Qatar has been mediating to salvage a truce it brokered in Saada last year.

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, pointed the finger at "the militias organised by Abdul-Malik al-Houthi and others."

His accusations on Al Jazeera were echoed by an Interior Ministry official on the official Saba news agency who blamed the attack on "terrorist, criminal elements loyal to the terrorist Abdul-Malik al-Houthi."

The governor of Saada, Motahhar Rashad, had earlier given a count of six dead and 35 wounded in the blast but a Yemeni security source put the death toll higher at "around 15" and said between 60 and 70 people were wounded.

NORTHERN CONFLICT

Hundreds of people have been killed and thousands have fled their homes in Saada since the conflict began. Seven Yemeni troops were killed late on Tuesday in an ambush by the rebels.

Houthi called on the U.S.-allied government to investigate objectively and suggested the authorities might be involved.

"We have the right, if it is going in this direction, to accuse the authorities of being behind this incident, especially as the city of Saada is under tight security measures," he said.

"There is tough security around this mosque and the area in general ... so how did this incident happen?"

Yemeni officials say the rebels want to return to a form of clerical rule prevalent in the country until the 1960s. The rebels say they are defending their villages against what they call government aggression.

One of the poorest countries outside of Africa, Yemen is struggling with several conflicts on top of its economic ills.

As well as fighting the Houthi revolt, the ancestral home of Osama bin Laden has cooperated with the United States on security since the Sept. 11, 2001 attacks on U.S. cities. Shells landed on a government compound near the Italian embassy in Sanaa on Wednesday. A similar attack hurt 13 schoolgirls near the U.S. embassy in March.

In the south, anger over perceived depredations exploded into riots this year that threatened to weaken the 1990 accord that united traditionalist north Yemen with the Marxist south. (Writing by Lin Noueihed; Editing by Matthew Jones)

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