At least 11 people have been killed and 36 others injured after a bomb attack on a police vehicle, Istanbul’s governor has said. The deadly explosion ripped through central Istanbul near a university and tourist sites during the morning rush hour.

“Seven law enforcers and four civilians have died in the attack,” Istanbul Governor Vasip Sahin told reporters. “Thirty-six people have been injured, three are in critical condition.”

Citing a police source, Turkish broadcaster NTV reported that some 14 people have been injured in the attack, eight law enforcers among them.

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Media said the explosion took place as a police vehicle was passing the area.

Four people have been detained for questioning in connection with the attack, AP reported, citing Turkish state media.

“There is no immediate claim of responsibility for the attack,” Turkish journalist Pinar Obabasi told RT, adding that the blast caused “a lot of damage.”

“Police are investigating the crime scene, with a security corridor set up,” she added.

A parked car stuffed with explosives was detonated by remote control as the police bus drove by, according to CNN Turk. Gunshots were heard in the area after the blast, Anadolu Agency said.

A Reuters’ witness reportedly saw what appeared to be two police vehicles hit.

Reports vary on the exact location of the explosion. According to CNN Turk, the bomb attack occurred in the central Istanbul district of Vezneciler. Turkish broadcaster NTV reported that a powerful blast took place in the city’s Beyazıt area.

No one has claimed responsibility for the attack so far, which happened during the morning rush hour.

Turkey’s Ihlas news agency has posted footage showing the aftermath of the explosion, with ambulances rushing towards the scene of the blast.

An Istanbul court has imposed a temporary ban on coverage of a number of details regarding the bomb attack, TASS reported, citing a statement from Turkey’s Supreme Council for Radio and Television. The ban has been introduced in order to “maintain public order, protect territorial integrity and prevent crime.” It concerns coverage of the ongoing investigation, footage showing the victims and those injured, police transcripts of talks, and demonstration of materials related to the suspects. The ruling covers all Turkish media. Similar measures were taken during previous terrorist attacks in Turkey.

A fresh wave of explosions has hit Turkish cities in recent months, including major urban areas.

A car stuffed with explosives detonated near military barracks in Istanbul in May, injuring eight people. The Turkish military blamed the attack on Kurdish fighters.

In March, 37 people were killed in a bombing near public bus stops in the Turkish capital, Ankara.