An explosion on an overpass near a metro station has injured at least five people in Turkey's largest city, Istanbul.
The explosion, which struck during rush hour on Tuesday afternoon, occurred near the Bayrampasa metro station, with authorities suspending services to the station immediately after.
Bayrampasa is a residential and industrial area on the European side of Istanbul.
Atilla Aydiner, the district mayor, and the state-run Anadolu news agency said a bomb caused the blast.
"Five of our citizens were injured when a pipe bomb left on barriers on the overpass exploded," Aydiner told A-Haber television.
Earlier reports suggested that a power transformer may have caused the explosion.
CCTV footage of the incident received by Dogan news agency showed large sparks shooting out like fireworks from the overpass as a train passed near the Bayrampasa station.
The explosion cracked the windows of the train and passengers were taken off and transferred on to lorries.
Although Istanbul's metro is largely underground, it runs above ground in some places, including around Bayrampasa.
Anadolu said police were investigating whether the bomb had been aimed at a police bus that was damaged in the attack.
"The cause of the explosion is not clear. We are investigating all possibilities," Vasip Sahin, the governor of Istanbul, was quoted as saying by Anadolu.
He said only one person had been injured in the blast.
"It was a large explosion, right in a central location and in a busy place but fortunately there was no loss of life."
Turkey has suffered a number of bombings over the past few months, including twin blasts at a peace rally in Ankara in October, which killed around 100 people.
Authorities blamed the Islamic State of Iraq and the Levant (ISIL) group for that attack.
Source: Al Jazeera and agencies