U.S. forces raided an insurgent facility that may have been producing an unspecified type of chemicals, the U.S. military said Saturday. It was unclear what was being produced or whether the materials were intended for weapons, the statement added.

U.S. troops, acting on a tip from detainees under interrogation, raided a "suspected insurgent chemical production facility (search)" in northern Iraq last Tuesday, the statement said, without specifying the location.

However, the military cautioned that ongoing testing at the facility was "insufficient to determine what the insurgents had been producing." The military said it also was investigating which insurgent group was operating the facility.

The military has found many suspected chemical sites in the past, none of which ended up containing chemical or biological weapons. Testing of such sites can take several days.

One of the main reasons stated for the U.S.-led invasion of Iraq (search) in March 2003 was to destroy Saddam Hussein's purported weapons of mass destruction. None were ever found.

The statement said officials were examining chemical evidence, but did not say if chemicals were stored at the facility.

"We are continuing to investigate the production and storage facilities to determine what type and quantities of chemicals were produced at the facility," said Col. Henry Franke (search), a nuclear, biological, and chemical defense officer with the multinational force.