Sana’a: Yemeni Shi'ite rebels opened fire on a military plane flying above the flashpoint city of Sa’ada, officials said on Friday, in one of the most serious breaches yet of a truce to end a northern war.

The plane, likely carrying military and government officials, was not hit in the shooting, which took place on Thursday, one official said.

"An Antonov military plane came under fire by [Al] Houthi elements as it was flying over the city of Sa’ada," a member of a committee overseeing the truce said, referring to the rebels by the clan name of their leaders.

"The plane usually does routine trips to transport military and administrative leaders to the (Sa’ada) province to carry out their work," the committee member added, calling the shooting a serious violation of the ceasefire.

The government, struggling to stabilise a fractious country where Al Qaida is trying to strengthen its foothold, agreed a truce in February with the northern rebels to halt fighting that has raged on and off since 2004 and displaced 250,000 people.

Yemen jumped to the forefront of Western security concerns after Al Qaida's Yemen-based regional arm claimed responsibility for an attempted attack on a US-bound plane in December.

Western governments and Saudi Arabia fear that Al Qaida is exploiting instability in Yemen to use the Arabian peninsula state, strategically located next to the world's biggest oil exporter, as a base for attacks in the region and beyond.

Last month, President Ali Abdullah Saleh, whose government is also trying to quell southern secessionists, declared the war in the north was over.

While the ceasefire has mostly held, previous truces have not lasted and analysts are sceptical whether this one will either, so long as Shi'ite complaints of discrimination by the state remain unaddressed.