ISTANBUL -- Two explosions struck Saturday night outside a soccer stadium in Istanbul after fans had gone home, an attack that wounded at least 20 police officers, Turkish authorities said.

One of the blasts was thought to be a car bomb, and the second appeared to have been caused by a suicide bomber.

Police cordoned off the area as smoke rose from behind the newly built Vodafone Arena Stadium, known as Besiktas Stadium after the local team and neighborhood. Witnesses also heard gunfire after the explosions.

The first and larger explosion took place about 10:30 p.m. after the home team Besiktas beat visitor Bursaspor 2-1 in the Turkish Super League.

Interior Minister Suleyman Soylu, who gave the casualty toll and said the wounded were police officers, rushed from Ankara to Istanbul.

There was no claim of responsibility for the attack. This year, Istanbul has witnessed bombings attributed by authorities to the Islamic State group or claimed by Kurdish militants.

"It is thought to be a car bomb at a point where our special forces police were located, right after the match at the exit where Bursaspor fans exited, after the fans had left," Soylu was quoted as saying by Turkey's state-run Anadolu Agency. "We have no information on the number of dead. God willing, we hope there won't be any."

Speaking later to reporters in Istanbul, he said the first explosion took place on a hill overlooking the stadium. The second explosion struck Macka Park and was believed to be a suicide bomb.

The private NTV channel reported the target of the first attack was a bus for riot police and said nearly 40 wounded were taken to a hospital.

Television images showed more than a dozen ambulances on a street hugging the stadium and a police helicopter flying overhead with searchlights. The window glass of nearby buildings was shattered by the blasts and coated the pavement. Investigators, including Istanbul police chief Mustafa Caliskan, were on the scene.

The Besiktas sports club "strongly condemned" terrorism and the attack in a statement posted on its website.

Bursaspor said none of the wounded was fans and issued a statement saying "we wish a speedy recovery to our wounded citizens."

Turkey's radio and television board issued a temporary coverage ban citing national security concerns.

It said "to avoid broadcasts that can result in public fear, panic or chaos, or that will serve the aims of terrorist organizations."

Prime Minister Binali Yildirim and Istanbul Governor Vasip Sahin were also notified about the attack, Anadolu said.