The military sources said the fighting was for control of a strategic military installation at the entrance to the northern province of Al-Jawf, which the rebels, also known as Huthis, have taken over.

"The battle began after noon on Sunday and continued until the evening," a tribal source said, adding various types of heavy weapons had been used in the fighting.

"The Huthis were able to gain complete control of the site, which had two tanks and a number of military vehicles in it," the tribal source said, adding there had been other clashes in the area in recent days.

A military aircraft was sent to attack the site but was shot down, killing the pilot, the tribal source said.

Yemeni authorities on Sunday announced that "a military training aircraft" had crashed in Al-Jawf.

Government forces have been engaged in sporadic fighting with the rebels in Yemen's north since 2004. A ceasefire between the rebels and government forces went into effect on February 12, 2010.

Protests calling for the ouster of Yemeni President Ali Abdullah Saleh have spread to the north.

Tens of thousands of supporters of the rebel group protested on February 21 in the north Yemen city of Saada to demand Saleh's departure, a tribal leader said.