Sana'a, Yemen  - Thousands of people have fled fighting between government forces and Shiite rebels in the north-western Yemeni province of Saada, the International Committee of the Red Cross (ICRC) said Sunday, and called the two sides to "spare the lives of civilians."

The army last week began a massive attack on strongholds of the rebels, known as Houthis, with airstrikes and artillery bombardments on mountainous area in Saada on the borders with Saudi Arabia.

The relief agency said in a statement received by the German Press Agency dpa that it was "alarmed about the intensification of armed confrontations in the north of Yemen over the past two weeks."

It said "thousands of persons" have fled the fighting to take temporary refuge in Saada and neighbouring province of Amran.

"The ICRC is worried about the safety of internally displaced persons in general, particularly those sheltered in some camps in Saada that are located in the vicinity of the fighting," the statement said.

It called on the government and rebels to take "all necessary to spare the lives of civilians and their properties," and to allow medical treatment for the wounded.

The organisation said it has a deployed a 45-member team to Saada, including five foreigners, to assess the humanitarian situation and respond to their needs in cooperation with the Yemeni Red Crescent Society.

Local sources in Saada, which located around 240 kilometres north of the capital Sana'a, said the army offensive continued for a sixth day on Sunday.

The sources told dpa that warplanes shelled Houthis bases in the the Haidan and Saqain districts of Saada.

Fighter jets also hit rebel targets in Malahid area in support of ground troops advancing in the area, the sources said.

The rebels said in a statement that they killed nine soldiers in confrontations in Malahid. Government officials refused to comment on the reported army fatalities.

The fighting has killed and wounded dozens, but a thorough tally for the casualties is not available.

On Friday, at least 16 Shiite rebels and five army soldiers were killed in fierce clashes in Harf Sufian district of Amran province, which borders the restive Saada province.

Authorities announced on Thursday six conditions for halting the army attack against the rebels, who refused the ceasefire terms, saying the peace offer was intended to "mislead the public opinion."

The country's Supreme Security Committee said last week that the assault was "the last option after the rebels rejected the call of peace made by the government."

It vowed to strike the rebels with an "iron fist" until they give themselves up to authorities.

Tensions have been rising between the Houthis and the army in Saada since last July, when President Ali Abdullah Saleh declared the conflict over.

Five waves of fierce fighting between the rebels and the military have left hundreds of soldiers and insurgents dead since 2004.

Authorities have accused the rebels of trying to reinstall the rule of imams, toppled by a republican revolution in northern Yemen in 1962.

The Houthis belong to the Zaidi sect, an offshoot of Shiite Islam. (dpa)