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Report: Blast at Istanbul subway station causes injuries

  • Riot police secure the area after an explosion on a highway overpass near a subway station, wounding five people, in Istanbul, Turkey, Tuesday, Dec. 1, 2015. The explosion was caused by a bomb left on barriers on the overpass, according to Atilla Aydiner, the mayor for Istanbul's Bayrampasa district.(AP Photo/Cagdas Erdogan)

    Riot police secure the area after an explosion on a highway overpass near a subway station, wounding five people, in Istanbul, Turkey, Tuesday, Dec. 1, 2015. The explosion was caused by a bomb left on barriers on the overpass, according to Atilla Aydiner, the mayor for Istanbul's Bayrampasa district.(AP Photo/Cagdas Erdogan)  (The Associated Press)

  • Riot police arrive after an explosion on a highway overpass near a subway station,  wounded five people and was caused by a bomb according to information given by the local mayor, in Istanbul, Turkey, Tuesday, Dec. 1, 2015. The bomb was left on barriers on the overpass, said Atilla Aydiner, the mayor for Istanbul's Bayrampasa district.(AP Photo/Cagdas Erdogan)

    Riot police arrive after an explosion on a highway overpass near a subway station, wounded five people and was caused by a bomb according to information given by the local mayor, in Istanbul, Turkey, Tuesday, Dec. 1, 2015. The bomb was left on barriers on the overpass, said Atilla Aydiner, the mayor for Istanbul's Bayrampasa district.(AP Photo/Cagdas Erdogan)  (The Associated Press)

  • A police forensic officer secures the area after an explosion on a nearby highway overpass near a subway station wounded five people and was caused by a bomb, in Istanbul, Turkey, Tuesday, Dec. 1, 2015. The bomb was left on barriers on the overpass, said Atilla Aydiner, the mayor for Istanbul's Bayrampasa district.(AP Photo/Cagdas Erdogan)

    A police forensic officer secures the area after an explosion on a nearby highway overpass near a subway station wounded five people and was caused by a bomb, in Istanbul, Turkey, Tuesday, Dec. 1, 2015. The bomb was left on barriers on the overpass, said Atilla Aydiner, the mayor for Istanbul's Bayrampasa district.(AP Photo/Cagdas Erdogan)  (The Associated Press)

Turkey's private NTV television says an explosion at an Istanbul metro station has caused some injuries.

The cause of the explosion wasn't immediately known. Subway services in Istanbul have been halted on the entire network.

The state-run Anadolu Agency said the explosion occurred at an overpass near the station, not in the station.