Ankara, Turkey (CBS News) --
A suicide bomber detonated his explosives at an entrance to the U.S. Embassy in the Turkish capital Ankara on Friday, killing at least one security guard.
A U.S. State Department official confirmed to CBS News that at least one guard had been killed in the attack.
The U.S. Ambassador was quoted by the Reuters news agency as saying the slain guard was a Turkish national, but that report could not be independently verified. U.S. Embassies are usually guarded by a combination of local security personnel and American diplomatic security forces.
An AP journalist reported seeing a body in the street in front of an embassy side entrance. It was not clear whether the victims of the blast were U.S. nationals, but they were identified as embassy security guards by the French news agency AFP.
The bomb appeared to have exploded inside a security checkpoint at an entrance to the embassy.
CNN's Turkish service said witnesses had seen the bomber approach the building and enter a gate to the fortified compound. It wasn't clear whether the bomber entered the building before detonating their explosives.
The switchboard for the U.S. Embassy is operated out of Istanbul. A switchboard operator told CBS News the embassy staff had taken cover following the explosion, explaining why nobody answered phones at the Ankara building.
The U.S. Embassy is located in the heart of Ankara. Photos and video broadcast by Turkish television showed significant damage to a wall and what appeared to be a bullet-proof window in the embassy.
Turkey is a vital U.S. ally in the region. The country shares borders with Iraq, Syria and Iran. A Kurdish separatist group, the PKK, has fought a bitter insurgency against the government for years in the south, but other terrorist organizations have been known to operate inside Turkey, including al Qaeda.
CBS News senior correspondent John Miller, a former deputy director in the National Intelligence Director's office, says al Qaeda will be one of the first groups considered as suspect in the attack, but he also notes the recent Israeli airstrike in Syria, for which Damascus and its staunch ally Iran vowed to retaliate.
Iran, Miller says, has extensive intelligence operations in Turkey, and its Islamic militant group ally, Hezbollah, also has significant assets there.
"Iran, in terms of retribution, would stack Israel and the U.S. together," says Miller.