By Mohamed Sudam
SANAA (Reuters) - Yemeni Shi'ite rebels opened fire on a military plane flying above the flashpoint city of Saada, officials said on Friday, in one of the most serious breaches yet of a truce to end a northern war.
The plane, which state media said was carrying military and government officials, was not hit in the shooting, which took place on Thursday.
"An Antonov military plane came under fire by Houthi elements as it was flying over the city of Saada," a member of a committee overseeing the truce said, referring to the rebels by the clan name of their leaders. The rebels denied involvement, Yemeni media said.
"The plane usually does routine trips to transport military and administrative leaders to the (Saada) province to carry out their work," the committee member added, calling the shooting a serious violation of the ceasefire.
The government, struggling to stabilize a fractious country where al Qaeda 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.
The shooting was one of the most serious breaches yet of the truce, and came just days after rebels shot dead a school guard and lost one of their own in a gunfight on Tuesday.
Yemen jumped to the forefront of Western security concerns after al Qaeda's Yemen-based regional arm claimed responsibility for an attempted attack on a U.S.-bound plane in December.
Western governments and Saudi Arabia fear al Qaeda 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 skeptical whether this one will either, so long as Shi'ite complaints of discrimination by the state remain unaddressed.
In addition to its conflict in the north, the government is also trying to quell secessionist demands in the south, where tensions between Yemeni security forces and separatists have been on the rise in recent months, accompanied by deaths and widespread arrests on both sides.
However Sanaa said the car bomb death of a retired army officer in south Yemen on Wednesday that also wounded his brother, a colonel, was the result of an accident and not an assassination by separatists.
The Interior Ministry said on its web site that the two men were repairing their car when a bomb they were carrying fell into the car and exploded, killing the officer and wounding the other. The ministry gave no further explanation.
North and South Yemen formally united in 1990 but many in the south, where most of impoverished Yemen's oil facilities are located, complain northerners have used unification to seize resources and discriminate against them.
(Reporting by Mohamed Sudam; Writing by Cynthia Johnston; Editing by Philippa Fletcher)