In a filing with US regulators last week, AstraZeneca said it had received a Department of Justice inquiry "in connection with an anti-corruption investigation relating to activities in Iraq."

The filing states the probe is at least partly related to a federal lawsuit filed in October on behalf of troops who were killed or wounded in Iraq in the 2005-2009 period, the height of the Iraq War insurgency.

Plaintiffs allege the firms, hoping to win business in Iraq, violated the US Anti-Terrorism Act and other laws by giving pharmaceuticals and medical supplies to the ministry of health when it was controlled by followers of Moqtada Sadr.

The powerful Shiite cleric, whose populist coalition triumphed at May elections, at the time ran death squads against Sunnis and is blamed for many attacks on US forces.

Sadr's Mahdi Army -- estimated to have had up to 60,000 members -- was once the most active and feared armed Shiite group in Iraq, and was blamed by Washington for thousands of killings.

According to The New York Times, the lawsuit claims Sadr's followers sold the medical supplies on Iraq's black market to fund such attacks.

Ryan Sparacino, a lawyer for plaintiffs in the case, told AFP on Wednesday that since 2004, "Iranian-backed terrorists have relied on corruption at the Iraqi health ministry to help fund terrorism in Iraq."

The lawsuit states the health ministry itself was used to launch attacks, smuggle weapons and gather intelligence, and that ministry employees played key leadership roles in the Mahdi Army.

In a statement, AstraZeneca said it "has a robust and dynamic compliance program, and we refuse to tolerate bribery or any other form of corruption."

The other firms listed in the lawsuit are General Electric, Johnson & Johnson, Pfizer, as well as Roche Holding A.G.

The Department of Justice did not immediately return a request for comment.