Yemeni rebels opened fire on a military plane flying above the flashpoint city of Saada, officials said 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 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 stabilixe 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 Tuesday.