A suicide bombing ripped through a famous shopping street in central Istanbul on Saturday, killing four people and injuring dozens a week after an attack by Kurdish rebels left 35 dead in Ankara.
The attack -- the sixth of its kind since July -- took place on Istiklal Caddesi, a pedestrian thoroughfare in the European side of the city that is usually thronged with shoppers, strollers and buskers but was still relatively quiet at the time of the blast.
"This is a suicide attack, a terrorist attack," Istanbul governor Vasip Sahin told reporters at the scene, giving a provisional toll of four dead. The bomber was also killed, he said.
Health Minister Mehmet Muezzinoglu said 36 people were injured, seven seriously. Twelve foreigners were among the casualties, he said, without giving their nationalities.
The device exploded near a shopping mall, around 500 metres from Taksim Square, a popular meeting point for Istanbul residents.
No group had yet claimed responsibility for the attack.
Sahin said the intended target was a nearby local authority building.
"We heard a strong explosion. We rushed to the window and saw body parts stuck to the window pane," Ahmet, who lives in a building across the street from the scene of the attack and who was later evacuated, told Agence France Presse.
Ahmet, a shoe shiner, said he was at Taksim Square when he heard "a loud explosion".
"I felt the ground shake and then saw police and ambulances rushing past," he said.
A large stretch of the street was evacuated after the attack. Armed police sealed off the area as shocked tourists looked on and a police helicopter hovered overhead.
CCTV footage published online by Dogan news agency appeared to show the moment of the blast, with a fireball erupting near a handful of passersby, sending them rushing for cover.
Television images showed ambulances ferrying the injured to hospital.
Turkey, which has been rocked by a string of attacks that have sharply increased in frequency since January, had been on high alert ahead of Kurdish New Year celebrations planned for Monday.
A Kurdish rebel group, the Kurdistan Freedom Falcons (TAK), claimed responsibility for an attack on March 13 on a busy transport hub in Ankara that killed 35 people and threatened further strikes on the Turkish state.
TAK, which also claimed a car bombing in Ankara in mid-February that killed 29 people, has ties to the separatist Kurdistan Workers' Party (PKK) against which the Turkish army is waging a major campaign in the south-east.
A court in Ankara on Friday evening remanded five people in custody on suspicion of links to last week's attack in the capital, which was carried out by a 24-year-old female student named by TAK as Seher Cagla Demir.
TAK said that bombing aimed to avenge members of the Kurdish minority killed during the military's offensive against the PKK and had not meant to target civilians.
On Thursday, President Recep Tayyip Erdogan vowed to "crush all the terrorists in this country."
Turkish airforce planes continued Friday to bomb PKK hideouts in mountains across the border in northern Iraq, an army statement said.
- Kurdish New Year fears -During the week, the U.S. embassy in Ankara had issued a warning to its citizens in Turkey to exercise caution ahead of the Kurdish Nevruz (New Year) celebrations, which have been a flashpoint for pro-Kurdish demonstrations in the past.
Turkey has also been repeatedly targeted in recent months by Islamic State (IS) jihadists operating out of neighbouring Syria.
IS was blamed for three other large-scale attacks in recent months, including a suicide attack in January in Istanbul in which 12 German tourists were killed and an attack on a peace rally in Ankara in October that claimed 103 lives.
On Thursday, Germany closed its embassy in Ankara, its consulate in Istanbul and German schools in both cities, citing "very serious" indications of planned attacks.
Embarrassed by accusations of security lapses, Erdogan has called for journalists, activists and intellectuals who criticize the army's tactics in battle-scarred Kurdish towns and cities to be designated "accomplices" of terror, causing an outcry over dwindling free speech.
Turkey's strongman president has also pushed for lawmakers from a pro-Kurdish party to be stripped of their parliamentary immunity so they can be prosecuted for "terrorist propaganda"