A massive explosion at a central metro station in Turkey’s largest city of Istanbul on Tuesday left at least five people wounded, according to the district mayor.

Bayrampasa district mayor Atilla Aydiner told A Haber television that a pipe bomb exploded on an overpass near the subway station wounding five, contradicting earlier reports that indicated at least one person was killed.

Emergency medical services were dispatched to the scene, after the blast that could be heard in various parts of the major, and which was timed for the evening rush hour.

The explosion occurred at Bayrampasa metro station, which was shut down after the blast. Associated Press reports the subway services were suspended throughout Istanbul as a result.

The Turkish Haberturk initially reported speculation that the blast may have been caused by a blown power transformer, although the Turkish NTV reported that the blast was caused by a bomb instead.

Aydiner’s revelation that a bomb caused the blast would strengthen suspicions that it was a terrorist attack.

Turkey has recently seen tensions with Russia skyrocket, after it shot down a Russian fighter jet on the Syrian border last week. Islamic State (ISIS) has also had a heavy presence in Turkey, which has been a key route for its fighters flocking to Syria.