The motive for the assault at Topkapi Palace was not immediately known. But police said the man had entered Turkey only three days ago. Turkey supported the popular uprising that defeated Muammar Qaddafi's regime.

Police also said the attacker arrived at the scene in a car with Syrian license plates. Minutes before the attack, Turkey's Foreign Minister Ahmet Davutoglu had announced tough economic sanctions on Syria to protest its government's crackdown on an 8-month-old pro-democracy uprising.

Multiple gunshots were heard from behind the high walls of the Topkapi Palace before the attacker was killed, and some tourists threw themselves on the ground to protect themselves, officials and witnesses said.

Topkapi Palace, the seat of the Ottoman sultans for almost 400 years, is located in the city's historic Sultanahmet district, which also includes the Blue Mosque and the former Byzantine church of Haghia Sophia.

Witnesses said the man shot the soldier in the leg and the guard in the abdomen before running into the palace courtyard through the main gate, shouting "Allah-o-Akbar!"