The U.S. military in Iraq says three Marines have died of wounds sustained due to enemy action in western Al Anbar province.

A statement issued Thursday said the Marines died Wednesday but did not provide further details.

Also Thursday, Iraqi witnesses said U.S. forces opened fire on a minibus in Baghdad, killing four people and wounding eight.

They say the bus was carrying workers through the city's Sadr City neighborhood. The U.S. military has not commented on the report.

And Iraqi officials say 100 people were killed in insurgent attacks and sectarian violence across the country Wednesday.

A U.N. report says more than 3,700 Iraqi civilians were killed in October -- the highest monthly toll since U.S. forces invaded the country in 2003.

Some information for this report was provided by AFP and Reuters