For nearly three months, Saudi Arabia, along with its allies, has been bombing Yemen, its southern neighbor, hoping to force the retreat of Shiite rebels who have seized major cities and to return the country's president from the Saudi guest mansion where he lives to the presidential palace. So far, it has not worked.

The Saudi-led military coalition fighting a rebel group in Yemen has in the past few weeks used cluster munitions supplied by the United States, Human Rights Watch said in a report released on Sunday. The report said video, photographs and other evidence showed that the coalition had used cluster bombs near villages in Yemen s northern Saada Province. The group, which said it had found evidence that the weapons had been deployed on at least two separate occasions, has not been able to establish whether any casualties had resulted from their use, according to the report.

Saudi Arabia said Tuesday that it was halting a nearly month-old bombing campaign against a rebel group in neighboring Yemen that has touched off a devastating humanitarian crisis and threatened to ignite a broader regional conflict. The announcement followed what American officials said was pressure applied by the Obama administration for the Saudis and other Sunni Arab nations to end the airstrikes.

The aircraft carrier Theodore Roosevelt and a guided missile cruiser were headed to the waters off Yemen on Monday to join 10 other American warships as a warning to Iran about its shipments of weapons to rebels there, American officials said. The Obama administration cast the deployment primarily as a show of force, but acknowledged that the flotilla could be used to interdict any supplies of Iranian arms to the Houthi rebels. The warships are also meant to reassure Saudi Arabia, an American ally that has been carrying out a bombing campaign against the rebels in Yemen.

The Saudi-led military intervention in Yemen threatens to turn what has been a civil war between competing branches of Islam into a wider regional struggle involving Iran. It could also destroy any hope of stability in Yemen. Even before the Saudis and their Arab allies started the bombing, Yemen was in severe distress; on Tuesday, the United Nations high commissioner for human rights warned that it is now on the brink of collapse.