WASHINGTON - U.S. officials confirmed Turkish media reports Friday that two Tunisian men had been detained in Turkey in connection with the killing of Ambassador J. Christopher Stevens and three other Americans in the attack on a U.S. diplomatic post in Libya on Sept. 11.
But the officials said they were awaiting more information from the Turkish authorities, and it remained unclear whether the two were considered to be suspects or witnesses in the violent attack in Benghazi, which fell on the 11th anniversary of the 2001 terrorist attacks.
Kanal D, a private Turkish television network, said the two were stopped at Ataturk Airport in Istanbul on Wednesday as they tried to enter the country using false passports.
Another report, in the Turkish newspaper Sabah, said that immigration officials had matched the names of the men, who were said to be in their mid-30s, to a list of possible suspects that U.S. intelligence agencies had given to security services in the region.
State Department spokesman Mark C. Toner said that U.S. officials "have been in contact with the Turkish government on this issue" but referred more detailed inquiries to the FBI. Asked about the detained Tunisians, an FBI spokesman, Paul E. Bresson, said officials were not ready to discuss the case.
President Obama has repeatedly pledged to "bring to justice" those responsible for the deaths of Stevens, a popular ambassador whose death provoked a protest by Benghazi residents, as well as Sean Smith, a computer specialist, and Tyrone S. Woods and Glen A. Doherty, both former members of the Navy SEALs.
But investigators have faced many obstacles. So far, Libyan officials have issued sometimes conflicting reports about arrests that offer little hard information. And security concerns had prevented an FBI team from visiting Benghazi until Thursday, when they spent several hours on the scene of the attack.
At a news conference Thursday, Attorney General Eric H. Holder Jr. declined to comment in detail on the investigation. But he suggested that the FBI team's limited access to the crime scene in Benghazi had not prevented investigators from following other leads.
"You should not assume that all that we could do or have been doing is restricted solely to Benghazi," Holder said. "There are a variety of other places in the country and outside the country where relevant things could be done and have been done."
U.S. investigators have been compiling information on the militants implicated in the attack, drawing in part on eyewitness accounts and interviews with attackers identifying some as members of a local militia, Ansar al-Shariah.
That raises questions about what kind of role the detained Tunisians might have played.