An explosion hit Istanbul's Beyazit district at the Vezneciler metro station as a riot police shuttle bus was passing on Tuesday morning.

The explosion took place at the metro station close to Istanbul University at around 8:30 am, the Daily Sabah reported.

Five police officers, including one who is in critical condition, have been reported as injured.

A number of gunshots were reportedly heard after the explosion but it has not been confirmed whether there was a clash or not.

Ambulances have been dispatched to the scene and the injured have been transported to nearby hospitals. The cause of the blast remains unknown. There has been no claim of responsibility for the blast.

Turkey has been a target for the PKK, Daesh and DHKP-C terror groups in recent months.

Two suicide bombs in October, 2015 outside Ankara's main train station as people gathered for a peace rally killed more than 100 people. It was Turkey's deadliest attack. The prosecutor's office said the attack was carried out by a local Daesh cell.

On January 12, Daesh targeted Istanbul's Sultanahmet, concerning which the city's governorate released a statement saying that 10 were killed and 15 injured in the blast.

On February 17, a bomb was detonated while military service vehicles were passing by killed at least 28 civilians and military personnel and injured 61 others in capital Ankara. The official statemens said the Syrian terror group YPG was behind the attack.

On March 19, a Daesh suicide bomber killed four people and injured 36, many of whom were foreigners, on Istanbul's tourist-heavy Istiklal street on a Saturday.

Source : MENA