AT least five people have died and dozens of others been injured after a suicide attacker detonated a bomb on Istanbul's main pedestrian shopping street.
The explosion occurred outside a local government office on Istiklal Street, which is also home to cafes, restaurants and foreign consulates. Tourists are thought to have been caught up in the blast.
CCTV posted to the internet showed the man casually strolling into the middle of the street while people walked by, before detonating an explosive concealed in his jacket.
The Turkish Ministry of Health said 36 people were injured, 12 of them critically. One of the casualties was said to be a woman from Israel, as were five of the wounded.
Two were also said to be from Ireland, while one person each from Iceland, Germany, Dubai and Iran were also among those injured.
Turkey was already on edge following two recent suicide car bomb attacks in the capital, Ankara, which were claimed by a Kurdish militant group that is an off-shoot of the outlawed Kurdistan Workers' Party, or PKK.
The most recent bombing attack, on March 13, targeted bus stops on Ankara's busiest street, killing 37 people including two bombers.
Turkish Prime Minister Ahmet Davutoglu convened a security meeting in Istanbul following the attack.
His deputy Numan Kurtulmus said: "It is clear that some people are giving logistic support (to terrorists), that some are giving political support and that they are even providing financial support as well as arms."
There was no immediate claim of responsibility for the attack.
A senior government official said authorities were still trying to determine who carried it out, with suspicion focusing on both Kurdish militants and the Islamic State group.
Police swiftly sealed off the area as ambulances and a forensic team rushed to the scene.
"It was one loud explosion," said Muhammed Fatur, a Syrian who works at a butcher shop near the scene of Saturday's explosion.
"Police came to the scene and sealed off the area."
Uwes Shehadeh was 500m (1,640ft) away when he heard "a horrific and horrible noise".
"People didn't know what was going on. It was very chaotic. Everyone was screaming and running away," he said. "Istanbul is on high alert and people are very worried as to what will happen next."
British singer Skin wrote on Facebook said the blast went off near her Istanbul hotel and that buildings "shook like paper".
She also expressed solidarity with the "innocent people and their families caught in this evil situation".
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