At least six people were killed and 53 others injured when an explosion hit Istanbul’s popular pedestrian Istiklal Avenue on Sunday. The casualties were confirmed by official sources.

"The relevant units of our state are working to find the perpetrators behind this heinous attack," President Recep Tayyip Erdoğan in a press conference before his departure for Indonesia to attend the G-20 summit.

"Initial observations show a woman played a role in the explosion," he said and stated that "based on initial information from the governor, the explosion could be suspected act of terrorism."

The Turkish president also vowed that those who waged terrorism against the Turkish nation would fail.

Images shared on social media at the time of the explosion indicated it could be heard from far away and that there were also flames.

Footage showed ambulances, fire trucks and police at the scene, and the area has been evacuated.

The cause of the explosion is still unknown.

In an earlier confirmation, on social media, Istanbul Gov. Ali Yerli Kaya said: "According to initial reports, in the explosion that took place on Istiklal Avenue, 4 people lost their lives and 38 people were injured. Our wounded are being treated. We wish God's mercy on those who lost their lives and a speedy recovery to the injured. Developments will be shared with the public."

In another post right after the attack, he wrote: "Today, at around 16.20, an explosion occurred in Taksim Istiklal Street in our Beyoğlu district. Our police, health, fire and (Disaster and Emergency Management Authority) AFAD teams were sent to the scene. There are casualties and injuries. Developments will be shared with the public," Daily Sabah reports.