ISTANBUL, Turkey (AFP) — Police have detained four suspects over an Istanbul car bombing that targeted a police bus yesterday, killing 11 people in the third deadly attack to strike Turkey’s biggest city this year.

The attack in Istanbul’s Beyazit district, close to major tourist sites, killed seven police officers and four civilians, State media said.

Another 36 people were wounded, three of them seriously, Istanbul Governor Vasip Sahin said.

UN chief Ban Ki-moon led international condemnation of the bombing, which his spokesman called a “despicable terrorist attack”.

The blast reduced the bus, which was carrying riot police, to mangled wreckage. It gutted the front of a hotel opposite and shattered the windows of nearby shops.

The four suspects were taken to police headquarters in Istanbul for interrogation, sState-run news agency

Anatolia agency said.

There was no immediate claim of responsibility for the attack.

But President Recep Tayyip Erdogan suggested the outlawed Kurdistan Workers’ Party (PKK), which has fought a three-decade insurgency against the Turkish State, was behind the attack.

For the PKK to target major cities such as Istanbul “is nothing new,” the president said after visiting the victims in hospital.

“We will fight against terrorists relentlessly to the end.”

He vowed in a later statement that the culprits would “pay the price for the blood they shed”.

Kurdish militants have repeatedly targeted Turkey’s security forces, but Islamic State (IS) jihadists have also staged attacks around the country in recent months, including in Istanbul.

This is the fourth bombing in Turkey this year to have killed more than 10 people, in a wave of attacks that has rattled citizens and dealt a heavy blow to tourism.

The bomb struck near Vezneciler metro station, within walking distance of tourist sites including the Grand Bazaar and Suleymaniye Mosque.

Reports said that shots were heard afterwards. Loudspeakers on mosques warned people to leave the area, and a controlled explosion was carried out on a suspicious vehicle.

The front of the upscale Celal Aga Konagi Hotel, a converted Ottoman mansion favoured by foreign tourists, was wrecked by the bombing, which left dust and debris scattered across the lobby.

The 16th-century Sehzade Mosque — considered one of the greatest masterpieces of Ottoman architect Mimar Sinan — was also damaged by the force of the explosion.

One local shopkeeper said his store had been “shattered in a thousand pieces”.

But he added: “The store is not the most important thing for us. There shouldn’t be any more terrorist attacks in our country. Damn them.

“We are ready to give up our shops as long as our lives are safe,” added the shopkeeper, who did not give his name. “We need peace in the country.”

Erdogan flew back to the capital Ankara later in the day and chaired a security summit at the presidential palace, with several ministers as well as the top army general and spy chief.

The United States and European Union condemned the attack, with the US Ambassador to Turkey, John Bass, saying in a

Twitter message: “Such senseless violence could never be rationalised by any cause.”

The United States will “continue to stand shoulder-to-shoulder with Turkey in the fight against terrorism”, Bass said.

French President Francois Hollande said the attack should strengthen common resolve to fight terrorism, while German Chancellor Angela Merkel and NATO chief Jens Stoltenberg also expressed solidarity.

Turkey has been waging an intense offensive against PKK militants in the southeast following the collapse of a two-year ceasefire last year.

Hundreds of members of the Turkish security forces have been killed in attacks since then, but civilian deaths in the conflict have rarely been confirmed.

A radical splinter group of the PKK, the Kurdistan Freedom Falcons, claimed responsibility for two bombings in Ankara earlier this year that killed dozens of people.

Over 40,000 people have been killed since the PKK took up arms in 1984 demanding a homeland for Turkey’s biggest minority. The group has since pared back its demands to focus on cultural rights and limited autonomy.

Turkey has responded defiantly to the attacks, vowing to overcome the threat both from the PKK and IS.