Five leading Republicans on the Senate Judiciary Committee are pressing Attorney General Eric Holder on whether he intends to use the federal civilian court system to prosecute an alleged Hezbollah operative linked to Iran, according to a letter from the senators to Holder obtained by Fox News.

The letter, dated Monday, reads in part: "We are deeply concerned that the administration and the Department of Justice are moving forward with plans to prosecute Ali Mussa Daqduq in federal court for clear violations of the laws of war that occurred in Iraq."

Holder, after reluctantly agreeing to send other high-profile terror trials to military tribunals at the Guantanamo Bay detention facility in Cuba, now faces a similar debate about the Daqduq case.

“It's certainly an important case, it's certainly a test case, it's certainly a case that that might set a precedent,” Sen. Orrin Hatch, R-Utah, told Fox News.

Click here to read the letter.

Hatch and the other four senators say in the letter they think Daqduq -- who is alleged to be a senior Hezbollah field commander -- should be tried at a Guantanamo Bay military court because he is accused of training Iraqis to use IEDs, and he is blamed for the execution of five U.S. soldiers in Karbala, Iraq.

One federal source said the Justice Department thinks Daqduq does not fall under the revised Military Commissions Act because he is not an Al Qaeda or Taliban operative.

The Heritage Foundation's Cully Stimson, an expert on military justice, says the case is clearcut.

“An 8th-grader can read the statute. It (pertains to) people who have taken up arms against the United States or its coalition partners during war time. This Dakduk individual clearly fits with that," Stimson said.

The attorney general's supporters, including Human Rights Watch, say Holder should send the case to federal court -- where these terrorism cases belong.

“This person is accused of killing U.S. military while they were in captivity,” Laura Pitter of Human Right Watch told Fox News. “And that is a war crime. And it is prosecutable in federal court."

A Justice Department spokesman had no comment on the senators' letter. Though the Obama administration has reversed course and will now try Khalid Sheikh Mohammed and his four alleged 9/11 co-conspirators in a military court, it seems the debate over where to prosecute alleged terrorists -- who are picked up on the battlefield -- is still not over.