WASHINGTON, June 24 (Reuters) - The U.S. Supreme Court

gave boost on Monday to a challenge by 21 pharmaceutical and

medical equipment companies led by AstraZeneca ( AZN ) to a

lawsuit accusing them of illegally helping to fund terrorism

that killed or injured hundreds of American troops and civilians

in Iraq.

The justices threw out a lower court's ruling that revived a

lawsuit brought by the military personnel and civilians who said

they were harmed between 2005 and 2011 in the Iraq war. The

justices asked the lower court to reconsider the case.

Hundreds of American service members and civilians, and

their families, sued the defendant companies, part of five

corporate families - AstraZeneca ( AZN ), Pfizer ( PFE ), GE

Healthcare USA, Johnson & Johnson and F. Hoffmann-La

Roche.

The plaintiffs accused major U.S. and European

pharmaceutical and device makers of providing corrupt payments

to the Hezbollah-sponsored militia group Jaysh al-Mahdi in order

to obtain medical supply contracts from Iraq's health ministry.

The plaintiffs alleged the militia group controlled the health

ministry.

The lawsuit, brought in 2017 in federal court in Washington,

seeks unspecified damages under the Anti-Terrorism Act, a

federal law that allows Americans to pursue claims related to

"an act of international terrorism."

A federal trial judge in 2020 dismissed the lawsuit, but the

U.S. Court of Appeals for the District of Columbia Circuit in

2022 overturned that decision and let the case move ahead.

The companies have denied wrongdoing and said they "are not

responsible in any way for the tragic events that were caused

and carried out by Iraqi militia groups."

The companies said in a filing to the justices that a 2023

Supreme Court ruling shielding social media platform Twitter,

now called X, from liability under the federal Anti-Terrorism

Act should bar the claims in this case.

In the Twitter case, the Supreme Court determining that

aiding-and-abetting claims under the Anti-Terrorism Act require

showing that a defendant "consciously and culpably" participated

in a terror act to help it succeed.

The plaintiffs countered in a filing that those who sued

Twitter had sought to hold that company liable for "mere

inaction" - the alleged failure to exclude a terrorism group

from the platform.

The pharmaceutical and device makers' "knowing bribes to

terrorists were far more culpable," the plaintiffs said.