SANAA: A Yemeni military source said on Saturday dozens of people were killed or wounded in clashes between Shiite rebels and the army overnight after a ceasefire broke down after just four hours.

"The armed forces and rebels engaged in violent clashes overnight which continued until dawn on Saturday in Malaheez and Hafr Sufyan" in Saada province, the source told AFP in Sanaa by telephone.

"Dozens of people have been killed and wounded in both camps," the source added, without elaborating. No official confirmation of the toll was available.

The government announced on Friday evening that it would declare a ceasefire in response to requests from aid agencies to help ensure the safety of civilians and to an offer from the rebels to cooperate in that effort.

In a statement on Friday, the Zaidi rebels said they were ready to cooperate with a UN plan for a "humanitarian corridor" to allow aid into areas where fighting is taking place.

The government suspended its three-week-old operation "Scorched Earth" and calm briefly returned to mountainous Saada province, stronghold of the rebels.

But the ceasefire did not last long. Government security officials said the insurgents -- also known as Huthis -- resumed operations overnight.

The Zaidi rebels "planned an attack on army positions, and the army responded," a military source said.

They "broke (the ceasefire) and resumed their acts of sabotage in the Malaheez and Hafr Sufyan regions" of Saada, a spokesman for Yemen's senior security commission said in a statement published early on Saturday.

"They will suffer the consequences" of their actions, he said, adding that the rebels broke the ceasefire less than four hours after the government announced it had begun at 1800 GMT.

The brief halt in hostilities came hours after the military said three rebel leaders had been killed in an attack in Malaheez at dawn on Friday.

Several vehicles delivering weapons and food to rebel strongholds in Saada province were destroyed or damaged in that assault, and security forces removed barriers the rebels had put across main roads to halt the army's advance, the military added.

The United Nations refugee agency UNHCR has said Saada city is practically cut off from the outside world, and called for humanitarian corridors to allow people out and aid in.

"The situation is deteriorating by the day," a UNHCR spokesman said last month, estimating that more than 35,000 people have been displaced in the latest fighting.

No figures have been published on the number of people killed since the military offensive began on August 11.

On Wednesday rebel leader Abdel-Malek al-Huthi threatened a war of attrition after the government rejected his offer of a truce.

"The authorities have missed the chance" to end the confrontation and "they will be responsible for the consequences of the war," he said.

An offshoot of Shiite Islam, the Zaidis are a minority in mainly Sunni Yemen but form the majority community in the north. They want to restore the immate overthrown in a 1962 coup.

The government is also confronted by growing separatism in the former South Yemen, and the impoverished Arabian peninsula country is increasingly being used as base by Al-Qaeda, taking advantage of its rugged terrain.