The UN chief called for a more thorough investigation into the July 30 attack which had resulted in heavy civilian casualties, including at least 28 people dead, 16 of whom were children.

Annan made his assessment in a letter to the Security Council calling for more information on the attack, and it drew on official accounts provided by the governments of Lebanon and Israel, as well as UN witnesses who visited Qana after the incident, although he highlighted that none were present when it occurred.

"The attack on Qana should be seen in the broader context of what could be, based on preliminary information available to the United Nations, including eyewitness accounts, a pattern of violations of international law, including international humanitarian law and international human rights law, committed during the course of the current hostilities," Annan said.

"I support calls for a more comprehensive investigation" into the Qana attack, he said.

"I have repeatedly condemned all actions that target civilians and I again call on all parties to the conflict to respect their obligations under international humanitarian law and, in particular, to take all necessary precautions to spare civilian life and property," the UN chief said.

Expressing his grave distress at the "tragic events" in Qana and by the overall effect of the conflict on the civilian populations of both Israel and Lebanon, Annan said it was at a "level of seriousness that requires further gathering of information, including violations of international humanitarian law and international human rights law."

His letter also included a statement from the International Committee of the Red Cross and highlighted that while medical teams from the UN Interim Force in Lebanon (UNIFIL) were able to assist in the rescue efforts once they arrived in Qana, the nearest UN post is around 20 kilometers away.

"UNIFIL is not in a position to confirm or deny whether Hezbollah was launching military activities from Qana in the days prior to or on 30 July," Annan wrote in the six-page letter that also includes excerpts from statements received from the governments of Israel and Lebanon.

"Qana is the center of Hezbollah's regional headquarters. It contains extensive weapons stockpiles, serves as a haven for fleeing terrorists, and is the source of over 150 missiles launched into northern Israel," Israel said in its statement, adding that "prior to the operation" it had "publicly called on the residents to move away from the terrorists and flee from the areas where missiles are being launched."

Lebanon's response contradicted this, noting that civilians had taken refuge in the three-storey building that was struck by Israeli missiles because it had a reinforced basement and adding that "they were not able to flee the area because of destroyed roads and the ongoing Israeli attacks."

"None of the bodies recovered showed that there were militants mingled among the civilians, and the rescuers found no weapons in the building that was struck," the Lebanese said.

Annan's letter also highlighted that Qana is no stranger to tragedy, noting that in April 1996, more than 100 Lebanese civilians who had sought refuge in a UNIFIL compound were killed by Israeli shelling.

The UN Security Council last week adopted a presidential statement on the Qana attack, expressing "extreme shock and distress" and requesting Annan to submit a report on the killings within seven days.

Preliminary reports put the death toll at more than 50 as the result of the deadly attack which occurred in the early hours of July 30 but a later count cut the toll by half. The house in which the civilians in Qana lived collapsed under the impact of one direct hit by a Israeli missile, a Lebanese government report said.