SANAA: More than 80 civilians were killed when an air raid blasted a makeshift camp of displaced people in northern Yemen, witnesses said on Thursday, as the army pursued its offensive on Shiite rebels.

One witness told AFP by telephone that most of those killed in Wednesday's raid were women and children.

A "warplane targeted displaced families who had gathered under trees in the area of Adi," in Amran province, the scene of heavy fighting between the army and the rebels, the witness said.

Another witness told AFP "at least 87 were killed" in the attack, which was acknowledged by a Yemeni official.

"The jet fighter targeted Huthi (rebels) who were firing (while hiding) among the displaced people," the official told AFP, while declining to comment on the death toll.

A rebel statement condemned the attack, accusing the Sanaa government, which has vowed to crush the five-year-old rebellion, of committing a massacre.

"The bloodthirsty authorities have committed a new massacre," the statement said.

It said that at noon (0900 GMT) on Wednesday MiG warplanes had targeted displaced people gathering along the Barata road, close to Adi village near Harf Sufyan, which lies on the route linking Saada to the capital.

"Dozens were killed and the bodies were blown away by the impact of the strike," the statement said.

Meanwhile, a government committee will investigate claims that civilians were bombarded by aircraft in Harf Sufyan, a security official was quoted as saying by a website linked to the defence ministry.

The official accused the rebels of taking civilians as human shields in the latest confrontations with troops and preventing them from leaving conflict zones, which caused the death of eight people, according

The official denied that there were any displaced civilians in the Harf Sufyan area, calling it an area for military operations and a "gathering point for the terrorist elements.'

The army, which launched operation Scorched Earth against the rebels on August 11, said on Thursday it has delivered heavy blows "over the past hours."

A military commander claimed the army had killed and wounded many rebels, whom it accused of using civilians as human shields. He did not elaborate.

New York-based Human Rights Watch urged the government to "promptly and impartially investigate responsibility for any attacks on civilians."

It also urged all parties to the armed conflict in the region to "respect the prohibition under international law against targeting civilians."

The Al-Haq Shiite opposition party condemned the attack, alleging that is is part of "recurring massacres against the people of Saada and Harf Sufyan."

A statement slammed the "silence of the political parties and humanitarian organisations about the massacres being committed" in northern Yemen, and demanded a "transparent probe" into the air raid.

There has been no reliable source for the death toll in the ongoing fighting.

The government accuses the rebels of seeking to restore the Zaidi Shiite imamate which was overthrown in a 1962 coup that sparked eight years of civil war.

An offshoot of Shiite Islam, the Zaidis are a minority in mainly Sunni Yemen but form the majority in the north.

The Zaidi rebels are known as Huthis after their late leader, Hussein Badr Eddin al-Huthi, who was killed by the army in September 2004

Relief groups have warned of worsening humanitarian conditions among the tens of thousands of civilians forced from their homes by the latest fighting.

On Tuesday, the United Nations and the international Red Cross both called for an aid corridor to allow urgent relief supplies to reach civilians.

The rebels said the same day they were "ready for an unconditional ceasefire" in a letter addressed to UN Secretary General Ban Ki-moon, a copy of which was received by AFP.

But the government has insisted that the rebels fulfill six conditions it had stipulated in an earlier truce offer, including their full disarmament.