Five detainees who are believed to be American citizens are being held in U.S. military detention facilities in Iraq after their arrests there over the past few months, the first Americans taken into custody during the war in Iraq on suspicion of aiding the insurgency or for terrorist activity, Pentagon officials said yesterday.

In addition to one detainee with dual U.S.-Jordanian citizenship who was arrested in late October, coalition forces have snared four suspects since April in unrelated cases involving potential insurgent activities throughout Iraq, said Bryan Whitman, a Pentagon spokesman. Three of those arrested are Iraqi Americans and one is an Iranian American who said he was in Iraq to film footage for a historical documentary.

All of those arrested held dual citizenship, but defense officials would not identify the detainees by name or divulge where they lived in the United States. It was also unclear yesterday how involved the detainees were in the fight against the coalition.

Whitman said one of the Iraqi Americans was arrested for "engaging in suspicious activities," another for alleged involvement in a kidnapping, and the third for "having the knowledge of planning associated with attacks on coalition forces."

The Jordanian American, arrested after a search of his Baghdad home in late October, is believed to be a high-ranking associate of Abu Musab Zarqawi's terrorist network. Officials described him as an emissary with intimate knowledge of and participation in terrorist activities in Iraq.

But in the case of the Iranian American -- 44-year-old Cyrus Kar of Los Angeles -- lawyers who are working to return him to his home in the United States argue that he was arrested by mistake as he was traveling through Iraq in a taxi while working on a film documentary about Cyrus the Great, the ancient Persian king. Kar, a native Iranian who served three years in the U.S. Navy, was arrested by Iraqi security forces almost immediately after he entered Iraq from Iran on May 17, when soldiers found several washing machine timers in the taxi's trunk.

Those timers can be used on improvised bombs, military officials said, and are a trademark of insurgents who have launched attacks on coalition forces throughout the country. The soldiers took Kar, his Iranian cameraman and the taxi driver into custody, and Kar eventually landed at Camp Cropper, the highest-level U.S. detention facility in Iraq.

Kar's story, which is detailed in a legal petition filed in federal court in the District yesterday, was first reported by the New York Times and the Los Angeles Times yesterday. In the court papers, Kar's family members allege that he has been held without reason for nearly two months and that the FBI has cleared him of wrongdoing after searching his home and files and after he apparently passed a polygraph test. But he remains behind bars in Iraq, without significant contact with the outside world, and with no charges filed against him.

"We don't understand why they won't let him come home, especially since the government said he hasn't done anything wrong," Shahrzad Folger, Kar's first cousin, said in a statement released yesterday.

Cathy Viray, a spokeswoman for the FBI field office in Los Angeles, said she was prohibited from providing any details about the Kar case. A U.S. law enforcement official in Washington confirmed that Kar's home was searched by the FBI, as alleged in the lawsuit, but declined to provide further details.

American Civil Liberties Union lawyers filed the petition yesterday, alleging that Kar is being held by the U.S. military "without the slightest hint of legal authority."

Lt. Col. John Skinner, a Pentagon spokesman who specializes in detention operations, said yesterday that all of the U.S. citizen detainees have been treated in accordance with the Geneva Conventions and have been treated humanely. All five of the detainees are at one of three main detention facilities -- Camp Cropper near Baghdad International Airport; at the Abu Ghraib prison west of Baghdad; or at Camp Bucca, near the southeastern port city of Umm Qasr.

Skinner said nationality is nearly irrelevant when people are taken into custody on suspicion of wrongdoing.

Pentagon officials said there are approximately 420 foreign nationals in U.S. detention facilities in Iraq, many of whom are Syrian, Saudi Arabian and Iranian, among many others. The American nationals make up a tiny fraction of the 10,000 detainees in custody, and an even smaller percentage of the more than 70,000 detainees who have been held in Iraq and Afghanistan since the wars began.

"If you're engaged in suspicious activities or acts, or with suspicious individuals, you're going to be scrutinized heavily, and nationality doesn't play a role in that," Skinner said.

But the American citizens' detention in U.S. military facilities raises distinct legal issues because the U.S. Supreme Court has ruled that even enemy combatants who are U.S. citizens deserve certain rights -- such as a legal status hearing and access to a lawyer -- rights the detainees have not yet been able to exercise. Whitman said such detainees fall into a "special category" but are not entitled to military commissions or legal representation, because they are being held as "imperative security" internees and have not been charged with a crime.

Whitman said there are several options for dealing with the five specific cases, and discussions are underway with Iraqi government and U.S. government officials. Ultimately, the cases could be transferred to either government. Whitman added that the detainees will have their detention and legal status reviewed by a three-member panel.

Staff writer Dan Eggen and researcher Julie Tate contributed to this report.

Shahrzad Folger, left, and Parvin Modarress, relatives of Cyrus Kar, at a Los Angeles news conference after the ACLU sued to try to force his release. Kar, 44, an Iranian-born U.S. citizen, is being held in Iraq.