SANAA (REUTERS) – Shi'ite rebels are to blame for the latest round of fighting with government forces that has engulfed swathes of northwestern Yemen this month, Foreign Minister Abubakr al-Qirbi said on Monday.

The resurgence of a conflict with so-called Houthi rebels that has flared intermittently since 2004 compounds the troubles of a country already grappling with secessionist violence in the south and a growing threat from al Qaeda militancy.

Qirbi said the rebels had taken President Ali Abdullah Saleh's unilateral declaration in July 2008 that the conflict was over as a sign of government weakness. They had ignored all invitations to renew dialogue and join reconstruction efforts.

Houthi fighters released by the government as a token of goodwill had returned to the mountains to resume training.

''Over the last six months they have tried to expand their influence,'' Qirbi told Reuters in an interview, accusing the insurgents of attacking government premises, occupying schools, blockading roads and extending their fight beyond their bastion in Saada province to the nearby provinces of al-Jawf and Hajjeh.

''In the end, things exploded and we have this war going on now,'' he said, declining to give casualty figures.

The rebels, adherents of the Zaydi branch of Shi'ite Islam -- a strongly tribal minority in mostly Sunni Muslim Yemen; oppose Yemen's close ties with the United States and say they are defending their villages against government oppression.

Yemeni forces have used air strikes, tanks and artillery in a week-old offensive described by officials as a determined attempt to crush the revolt, led by Abdul-Malik al-Houthi.

Scores of casualties have been reported since the conflict intensified in late July, but independent accounts of the fighting are rare. Journalists and diplomats are barred from the rugged mountain area near the Saudi border. The few aid agencies operating there are constrained by security concerns.

The insurrection in the north has underlined Western and Saudi fears that instability in Yemen may spiral out of control and allow al Qaeda militants to entrench themselves.

Qirbi said Yemen worked closely with Saudi Arabia and the United States in fighting terrorism. He welcomed signs that President Barack Obama's administration was moving away from its predecessor's habit of linking development aid with that issue.

''We would like a stronger and more transparent relationship as far as intelligence information is concerned,'' he said.

Washington should also appreciate that, as one of the poorest countries outside Africa, Yemen would have to divert money spent on fighting terrorism from development efforts.

''And, unless we combat poverty and create development, we are not going to succeed in combating terrorism,'' Qirbi said.

Strains emerged in US-Yemeni relations after a US drone attack killed an al Qaeda leader on Yemeni soil in 2002.

Other security hiccups, such as a prison break by 23 al Qaeda militants in 2006, have complicated the issue of how to deal with Yemeni detainees in the US jail at Guantanamo Bay, which Obama has promised to close by the end of this year.