Officials imposed a vehicle ban and closed all roads to the area for fear of further attacks.
Heet is in al-Anbar province, a past stronghold of opponents to the Iraqi government.
Violence in the province has fallen dramatically over the past year as the US military has cut deals with local Sunni tribal leaders against al-Qaeda in Iraq.
Government statistics show that 504 civilians were killed in al-Anbar in May, dropping from 966 in April.
The province had been used by the Iraqi government as an example of how peace could be brought to the whole country.