WASHINGTON -- A Hezbollah commander held in Baghdad by the U.S. military and considered a threat to American troops could be transferred soon to Iraqi authorities, and U.S. security officials worry he could escape or even be freed.

Ali Mussa Daqduq worked with Iranian agents to train Shiite militias who targeted American soldiers in Iraq, according to the U.S. military. He was captured in 2007 and U.S. officials have linked him to a brazen 2007 raid in which four American soldiers were abducted and killed in the Iraqi holy city of Karbala.

For years, The U.S. planned to try Daqduq in an American court, but that has stalled as the White House and Congress clashed over how to prosecute suspected terrorists.

Daqduq is one of about 10 remaining U.S. prisoners who, under a 2008 agreement between Washington and Baghdad, must be transferred to Iraqi custody by the end of 2011. Iraqi Justice Ministry spokesman Haidar al-Saadi said Wednesday that the transfer would happen by the end of the week. U.S. officials, however, said it probably won't be that soon.

Iraq's shoddy record on detainee security and its recent efforts to improve diplomatic ties with Iran have made U.S. authorities skittish about turning over Daqduq.

"He's the worst of the worst," said Bob Baer, a former CIA officer who has spent years tracking Hezbollah, a Shiite militant group linked to numerous terrorist attacks. "He has American blood on his hands. If released, he'll go back to shedding more of it."

In July 2010, just a week after the U.S. turned more than 1,000 detainees at its Camp Cropper prison over to Iraqi control, four Al Qaeda-linked detainees escaped. An investigation showed that the detainees had inside help.

The same was true again in May in an aborted escape from one of Baghdad's most heavily fortified prisons that left 17 inmates and guards dead, including a counterterrorism general.

Al-Saadi scoffed the notion that Daqduq would escape.

"Iraqi authorities are fully prepared to prevent any escape attempt, and Iraqi security forces are able to keep all detainees under control," he said.

It's possible, however, that Daqduq might simply walk free. The U.S. captured tens of thousands of terror suspects during the war and most were ultimately released by Iraqi authorities because of little evidence tying them to crimes.

Abdul-Rahman Najim al-Mashhadani, director of the Hammurabi legal rights watchdog group in Baghdad, said it's likely Daqduq will never be convicted in an Iraqi court.

"It will be difficult to provide evidence incriminating him for killing Iraqis because he was arrested by U.S. forces acting against U.S. forces only," al-Mashhadani said Wednesday.

Under President George W. Bush, U.S. officials envisioned the day when they could no longer detain Daqduq in Iraq. So they developed a plan in which military and intelligence officials questioned Daqduq, then let an FBI team start the questioning over from scratch. That way, he could someday be brought to a U.S. court and his statements could be used against him.

That plan has been scuttled, however, by Bush's Republican allies in Congress. They objected to Daqduq and other terrorist suspects being brought to the United States for trial.

Republicans want Daqduq and other suspected terrorists to be prosecuted at the Guantanamo Bay military base, which the Obama administration has tried to close. In a letter in May, Republican members of the Senate Judiciary Committee told Attorney General Eric Holder that they were "deeply concerned" that Daqduq might be prosecuted in the United States.

Lawyers who have reviewed the case concluded that while prosecuting him at Guantanamo Bay is possible, incarcerating him there is not. That's because Congress authorized military action against Al Qaeda and those who carried out the Sept. 11 terrorist attacks. The Supreme Court has relied on that authorization to allow the military to hold Al Qaeda suspects at Guantanamo Bay.

Hezbollah, considered by the U.S. to be a terrorist organization, is a Shiite Muslim group. Al Qaeda is a Sunni organization. The two have had a relationship of convenience at times but the 9/11 Commission found no evidence that Hezbollah was aware of or involved in the planning for the attacks on the World Trade Center and Pentagon.

A spokesman for the U.S. military in Iraq, Army Col. Barry Johnson, said the U.S. was "not under pressure to resolve this this week" and referred questions to the Justice Department. Justice Department spokesman Dean Boyd had no comment. The White House also had no comment.

The Justice Department has successfully prosecuted terrorists in criminal courts for years and has won life sentences for those involved in the 1993 World Trade Center bombing and the 1998 attacks on U.S. embassies in Africa. Even after 9/11, the Bush administration made criminal trials a key part of its strategy for fighting terrorists in Colombia.

But it became a political issue when Obama tried to bring 9/11 mastermind Khalid Sheik Mohammed to New York for trial. Congressional opposition torpedoed that plan and lawmakers responded by prohibiting the administration from prosecuting Guantanamo Bay detainees inside the United States.

In this politically charged environment, prosecuting Daqduq in a criminal court carries unusual risk. Evidence gathered in a war zone is almost always imperfect and U.S. counterterrorism officials worried that if they brought the case and lost, Congress would respond with even more restrictions on the Justice Department.