WASHINGTON - The United States has identified five men who might be responsible for the attack on the diplomatic mission in Benghazi, Libya, last year, and has enough evidence to justify seizing them by military force as suspected terrorists, officials say. But there isn't enough proof to try them in a U.S. civilian court as the Obama administration prefers.

The men remain at large while the FBI gathers evidence. But the investigation has been slowed by the reduced U.S. intelligence presence in the region since the Sept. 11 attacks, and by the limited ability to assist by Libya's post-revolutionary law enforcement and intelligence agencies, which are still in their infancy since the overthrow of dictator Col. Moammar Gadhafi.

The decision not to seize the men militarily underscores the White House aim to move away from hunting terrorists as enemy combatants and holding them at the military prison in Guantanamo Bay, Cuba. The preference is toward a process in which most are apprehended and tried by the countries where they are living or arrested by the United States with the host country's cooperation and tried in the U.S. criminal justice system. Using military force to detain the men might also harm fledgling relations with Libya and other post-Arab-Spring governments with whom the United States is trying to build partnerships to hunt al-Qaeda as the organization expands throughout the region.

A senior administration official said the FBI has identified a number of individuals that it believes have information or may have been involved, and is considering options to bring those responsible to justice. But taking action in remote eastern Libya would be difficult. America's relationship with Libya would be weighed as part of those options, the official said, speaking only on condition of anonymity because the official was not authorized to discuss the effort publicly.

The Libyan Embassy did not respond to multiple requests for comment.

The FBI released photos of three of the five suspects earlier this month, asking the public to provide more information on the men pictured. The images were captured by security cameras at the U.S. diplomatic post during the attack, but it took weeks for the FBI to see and study them. It took the agency three weeks to get to Libya because of security problems, so Libyan officials had to get the cameras and send them to U.S. officials in Tripoli.