Around 15 people were killed and over 60 were wounded when a bomb hidden in a motorcycle exploded outside a mosque in Yemen's volatile northern city of Saada on Friday, a security source said.

The blast happened as worshippers, including army officers, were leaving the Salman Mosque after Friday prayers, officials and security sources said.

"It is a large mosque," the governor of Saada, Motahhar Rashad, told Al Jazeera. He earlier gave the Arab network an initial count of six dead and 35 wounded.

But a Yemeni security source, who declined to be identified, put the death toll higher at "around 15" and said between 60 and 70 people were wounded.

The security source said that the imam of the mosque, Askar Zaayl, was also the office manager of Ali Mohsen, Yemen's northern military commander who has led the government's fight against rebels loyal to Abdul-Malik al-Houthi -- a member of the Zaydi sect of Shi'ite Islam.

Mohsen was not in the mosque at the time of the blast though other Yemeni officers were.

It was not known who planted the bomb near the door of the mosque, but the northwestern province has been rocked by sporadic violence since a conflict broke out in 2004 between government forces and rebels loyal to Houthi.

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, who often clash with troops of the U.S.-allied Yemeni government and tribes loyal to it.

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.

Sunni Muslims form a majority of Yemen's 19 million population, while most of the rest, including Houthi and his supporters, are Zaydis.

Houthi's supporters, who are not believed to be linked to the Sunni Muslim al Qaeda oppose Yemen's alliance with the United States.

One of the poorest countries outside of Africa, Yemen has been struggling with several conflicts in addition to its significant economic challenges.

As well as fighting the Houthi revolt, Yemen has witnessed several attacks on oil installations, government compounds and French and U.S. ships. The ancestral home of Osma bin Laden has cooperated with the United States on security matters since the September 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 school girls near the U.S. embassy in March.

In the south, anger over perceived depredations exploded into riots earlier this year that threatened to undermine the 1990 accord that united traditionalist north Yemen with the Marxist south.

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The blast killed around 15 worshippers, injured over 60.

Rueters