ANKARA, Turkey -- A suicide bomber struck the American Embassy in Ankara yesterday, killing a Turkish security guard in the second deadly assault on a U.S. diplomatic post in five months.

Declaring the assault an act of terrorism, the U.S. government warned Americans to stay away from all U.S. diplomatic facilities in Turkey and to be wary in large crowds.

Turkish Prime Minister Recep Tayyip Erdogan said police believe the bomber was connected to a domestic leftist militant group. White House spokesman Jay Carney, however, said the motive for the attack and who was behind it was not known.

"We strongly condemn what was a suicide attack against our embassy in Ankara, which took place at the embassy's outer security perimeter," Carney said.

A Turkish TV journalist was seriously wounded in the 1:15 p.m. blast in the Turkish capital, and two other guards had lighter wounds, officials said. State Department spokeswoman Victoria Nuland said a man detonated a suicide vest at a security checkpoint used by staff.

"He came to this first point of access to the compound . . . where you have to have your ID checked, you have to go through security," Nuland said.

"The level of security protection at our facility in Ankara ensured that there were not significantly more deaths and injuries than there could have been," she said.

The state-run Anadolu Agency identified the bomber as Ecevit Sanli. It said the 40-year-old Turkish man was a member of the outlawed Revolutionary People's Liberation Party-Front, or DHKP-C, which has claimed responsibility for assassinations and bombings since the 1970s.

The group has been designated a terrorist organization by the United States but had been relatively quiet in recent years.

Hillary Rodham Clinton, in her farewell speech to State Department staff moments after she formally resigned as secretary of state, said, "We were attacked and lost one of our foreign service nationals."

She said she spoke with U.S. Ambassador Francis Ricciardone, "our team there and my Turkish counterpart. I told them how much we valued their commitment and their sacrifice."

Sen. John Kerry, the incoming secretary of state, also was briefed.

The U.S. Embassy building in Ankara is heavily protected and located near several other embassies, including those of Germany and France. U.S. diplomatic facilities in Turkey have been targeted previously by terrorists.

In 2008, an attack blamed on al-Qaida-affiliated militants outside the U.S. Consulate in Istanbul killed three assailants and three policemen.

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