Israel may have violated agreements with Washington on the use of US-made cluster bombs in its war with Hizbullah in Lebanon last summer, the state department said today.

The Bush administration must now decide what action, if any, to take against Israel for its use of the weapons against towns and villages from which Hizbullah fighters fired rockets.

Opinion among US officials was divided, the New York Times reported at the weekend. The paper said some middle-ranking officials at the Pentagon and the state department were arguing that Israel had violated prohibitions on using cluster munitions against civilian areas.

However, others in both departments thought Israel's use of the weapons was justified on the grounds of self-defence in a conflict that cost the lives of 159 Israeli soldiers and civilians, the paper said. At least 850 Lebanese died in the fighting.

Tough action from the US is believed to be unlikely because of the White House's staunch support for the Israeli government.

Cluster bombs scatter hundreds of small "bomblets", many of which fail to explode, over a wide area. Inquisitive children may later pick these up, or civilians could step on them.

Israeli forces dropped an estimated 1m cluster bomblets in southern Lebanon last summer, 90% of which were dropped (pdf) in the last three days of the conflict, the group Landmine Action reported in October.

Even if Israel is found to be in violation of its agreements with the US, it is up to George Bush to decide whether to impose sanctions unless Congress decides to take legislative action, a highly unlikely development.

The state department is required to notify Congress of even the preliminary findings of possible violations of the Arms Export Control Act, the statute governing arms sales. It began an investigation in August.

Whatever the US decides, Israel makes its own cluster munitions, so a cutoff of US supplies would be mainly symbolic.

In 1982, the Reagan administration imposed a six-year ban on cluster bombs sales to Israel after a congressional investigation found Israel had used the weapons in civilian areas during its invasion of Lebanon that year.

The UN and human rights groups strongly criticised Israel's use of cluster bombs at the end of the 2006 Lebanon conflict.

"What is shocking and completely immoral is 90% of the cluster bomb strikes occurred in the last 72 hours of the conflict, when we knew there would be a resolution," the UN humanitarian chief, Jan Egeland, said soon after the war ended.

However, Israel said the use of cluster bombs was in accordance with international law and that its forces had not targeted civilians.

"The IDF [Israel Defence Force] does not deliberately attack civilians, and takes steps to minimise any incidental collateral harm by warning them in advance of an action, even at the expense of losing the element of surprise," the Israeli foreign ministry said last summer.

Nevertheless, Israeli television reported in December that the military's judge advocate general was gathering evidence for possible criminal charges against military officers who may have given orders for cluster bombs to be dropped on populated areas.

According to the UN mine action coordination centre for South Lebanon, by December 19, 18 people had been killed and 145 injured since the August ceasefire.

The casualty rate has come down sharply. Immediately after the war, there were more than 30 casualties a week, but the figure now stands at around three or four.