Three police officers died when unknown gunmen opened fire on a guard booth in front of the consulate. Three of the attackers died and one escaped. Several Turkish police and civilians were injured.

No casualties were reported among consulate employees.

"(We) also appreciate Turkish President (Abdullah) Gul's condemnation of the attack and the support of Turkish officials in Ankara and Istanbul," State Department spokesman Sean McCormack said. "Our countries will continue to stand firmly together to confront the threat of terrorism."

McCormack called the Turkish police "the first line of defense" at the consulate, and "they acted with extraordinary courage in repelling this attack."

The spokesman said investigators didn't know who was responsible for what he called a "terrorist attack."

He said the consulate would be open for regular business Thursday, but not consular business.

"We'll deal with any emergency cases that may come up, but ... tomorrow won't be a regular day in terms of consular services," McCormack said.

The secure U.S. facility was built after militants linked to al-Qaida conducted suicide bombings that targeted two synagogues, the British Consulate and the HSBC bank in Istanbul in 2003, killing 58 people.