Police guard the entrance to Turkey's largest airport, Istanbul Ataturk, Turkey, following a blast June 28, 2016. [Photo/Agencies]

FLIGHTS RESUME

Ataturk is Turkey's largest airport and a major transport hub for travelers from around the world. Pictures posted on social media from the site showed wounded people lying on the ground inside and outside the international terminal.

A helicopter buzzed overhead as police evacuated the building. Dozens of passengers walked back down access roads with their luggage, trying to hail cabs. The U.S. embassy urged U.S citizens to avoid the area.

Authorities halted the takeoff of scheduled flights from the airport and passengers were transferred to hotels, a Turkish Airlines official said. Earlier an airport official said some flights to the airport had been diverted, although Yildirim said air traffic had later resumed.

In the United States, the Port Authority of New York and New Jersey reacted to the explosions by putting armed, high-visibility patrols at the three main airports in the New York metropolitan region.

Turkey has suffered a spate of bombings this year, including two suicide attacks in tourist areas of Istanbul blamed on Islamic State, and two car bombings in the capital, Ankara, which were claimed by a Kurdish militant group.

In the most recent attack, a car bomb ripped through a police bus in central Istanbul during the morning rush hour, killing 11 people and wounding 36 near the main tourist district, a major university and the mayor's office.

Turkey, which is part of the U.S.-led coalition against Islamic State, is also fighting Kurdish militants in its largely Kurdish southeast.

One person was killed on Dec. 23, 2015, when an explosion hit Istanbul's second airport, Sabiha Gokcen, located on the Asian side of the city. That attack was claimed by a Kurdish militant group.