Yemen declared a state of emergency in a northern province bordering Saudi Arabia late Wednesday, where the Yemeni army is waging a comprehensive offensive against Shi'ite Islamists, bringing the country to the brink of all-out civil war. A serious humanitarian crisis has developed in the fighting zone, with more than 130,000 people fleeing over two weeks of fighting. Government officials say that the rebels, who are part of the Zaydi branch of Shi'ite Islam, oppose Yemen's alliance with the United States and want to restore clerical rule that existed until the 1960s. Warplanes and artillery bombed the Saada province for a second straight day on Thursday, according to the rebels and local officials. The offensive in Saada province started on Tuesday, after the rebels claimed they had wrested more control of the region from Sunni-led government troops. Authorities in turn promised to crush the Shi'ite uprising "with an iron-fist." Saada has been the scene of a five-year rebellion by a Shi'ite minority that has further destabilized the country as it faces a resurgent threat from al-Qaida, a separate secessionist uprising in the south and an economic downturn from plunging oil prices. The latest attacks came a day after air force planes hit an outdoor market in the provincial town of Haydan as people were doing their early morning shopping, killing several civilians, according to rebels and local officials. They also claimed that in a renewed bombardment, with sorties overnight and into early Thursday, military planes bombed several other Saada towns and rebel positions. "Dozens" of people were killed and wounded, including in the towns of Sihar, Miran and Al-Maqash. A statement from the rebel leader Abdel Malik al-Hawthi, posted on the group's Web site, described the attack as "a mass carnage" and appealed to Yemen's political parties to condemn the government strikes. It said an unspecified number of civilians died and posted gruesome photos of victims allegedly killed in the bombardment. In addition to the state of emergency in the province, the government imposed a nightly curfew in Saada and other nearby towns. A government committee also set several conditions on the rebels for halting its offensive, including leaving their positions, laying down their arms and handing over soldiers and civilians captured in the fighting. On Wednesday, a local government official said 20 rebels were killed. A local Health Ministry official said 12 others died in fighting across Saada and 51 were wounded. Yemen's instability has been a key concern for both the US and Saudi Arabia, where newspaper editorials have been warning of regional impact of the troubles. A commentary this week in Asharq Al-Awsat, a London-based pan-Arab newspaper owned by the Saudi royal family, warned that "this disaster threatens Yemeni unity as a whole, as well as the security of Saudi Arabia and all Gulf Cooperation Council countries without exception."