The US State Department has begun an investigation into whether Israel violated agreements by using cluster bombs in civilian areas in Lebanon.
A White House official said the investigation would focus on whether US-made weapons were deliberately used against non-military targets.
According to the UN, US-made weapons have been found at as many as 300 sites in south Lebanon.
Cluster bombs spray large numbers of bomblets over a wide area and can remain unexploded, endangering civilians long after they are fired.
Israel however says its use of weapons conforms to international standards.
