(Updates with deaths among Houthi fighters)
SANAA, July 5 (Reuters) - The Yemeni air force bombed Shi'ite Muslim fighters north of Sanaa on Saturday in fighting that killed at least 70 people, local officials said, after a truce reached last month between the insurgents and government forces collapsed.
The fighting in northern Yemen, which has taken on a sectarian tone, is further destabilising a country struggling to overcome a range of problems including a secessionist movement in its south and the nationwide spread of an al Qaeda insurgency.
Shi'ite Houthi fighters, officially known as Ansarullah, blamed army units linked to the Sunni Muslim Islah party for breaking the June 23 ceasefire on Friday, when government troops advanced on an area in al-Jouf province, northeast of Sanaa.
A Yemeni government official said the army's advance on the town of al-Safra had been prompted by the failure of Houthi fighters to vacate positions in compliance with the ceasefire.
Tribal sources in al-Jouf, which is partly controlled by the Houthi rebels, said at least 10 Houthi fighters, five tribesmen and three soldiers had been killed in fighting on Friday.
The fighting later spread to the adjacent Omran province, where the Yemeni air force bombed Houthi positions around the provincial capital early on Saturday. Local officials said at least 40 Houthi fighters, four government soldiers and eight Sunni tribesmen had also died.
YEARS OF TURMOIL
Ansarullah said on its website that its fighters had managed to drive what it said were "takfiri" - a term used to refer to hardline Sunni Islamists - from several positions in Omran. But the Houthis gave no figures for casualties on their side.
U.S.-allied Yemen, an impoverished country of 25 million that shares a long border with the world's top oil exporter Saudi Arabia, has been in turmoil since 2011 when mass protests forced the veteran president, Ali Abdullah Saleh, to step down.
At least 200 people have been killed this year in battles pitting the Houthis - named after the tribe of their leader - against the government and its Sunni tribal allies.
Officials say the Houthis, who have fought several short but bloody wars with government forces since 2004, are getting weapons from Iran.
The Houthis deny this, and say they are fighting for autonomy and less U.S. interference in Yemen's affairs.
Washington and Gulf countries are worried that further instability in Yemen could allow Al Qaeda in the Arabian Peninsula (AQAP), the Islamist group's regional wing, to consolidate its position and launch attacks overseas.
In southeastern Yemen, the state news agency Saba reported that one soldier had been killed and four wounded on Saturday in a "terrorist" attack on a security compound in the Hajar area of Hadramout province. The agency gave no further details. (Reporting by Mohammed Ghobari and Mohammed Mukhashaf in Aden,; Writing by Sami Aboudi; Editing by Sophie Hares and Pravin Char)