SANAA (AFP) — Heavy fighting broke out Sunday as troops renewed attacks on the mountain stronghold of Shiite rebels in Yemen’s rugged north, military officials and witnesses said, amid worsening humanitarian conditions in one of the world’s poorest countries.

Army tanks fired salvos as armored cars blocked the entrances to the narrow alleys of the old city in Saada, stronghold of the Zaidi rebels, two days after a government-proposed ceasefire failed to last more than hours, officials said.

The rebels, who are seeking to restore traditional rule by clerics, returned fire on the army from a hideout in a fortress overlooking the old town. Shops were closed and residents stayed indoors.

“They (the army and the rebels) clashed and the police halted all traffic. I was not able to get to work,’’ Abdel-Qader, a clerk, told AFP by telephone.

The fighting began intensifying on Saturday, leaving dozens of people dead or injured in the north of Yemen, according to military officials.