A suicide bomber and a locally-hired U.S. embassy guard were killed in a "terrorist blast" outside the U.S. Embassy in Turkey today, Turkish and American officials said. The explosion, which occurred at a checkpoint at the rear entrance to the embassy in Ankara in the early afternoon local time, also wounded two other guards and at least one civilian, identified by Turkish Interior Minister Muammer Guler as a female journalist. State Department spokesperson Victoria Nuland told reporters it was too early to determine who exactly was behind the attack, saying U.S. and Turkish officials are going to "look into every single possibility." Nuland said several members of embassy staff, both American and Turkish, were injured by flying debris. READ: White House: Bombing At U.S. Embassy In Turkey A 'Terrorist Attack' Turkish Prime Minister Recep Erdogan said, "It was a sad event, but this attack should remind us the necessity to work against terror together." Nuland said the perimeter access point where the explosion took place was part of a steady stream of security upgrades made over the last decade. "This upgrade security saved lives," she said. The blast comes on the same day that Secretary of State Hillary Clinton is scheduled to step down from her post, allowing Sen. John Kerry (D-Mass.) to take the reins as State Department chief. Nuland said that Clinton "was briefed immediately" about the attack and was dealing with the situation as she said goodbye to longtime staff members. Kerry's staff was also briefed in real time, Nuland said. Five months ago U.S. Ambassador to Libya, Chris Stevens, was killed alongside three other Americans in an attack on a U.S. diplomatic facility in Benghazi, Libya.