Police believe that Saturday's attack on Istiklal Street, Istanbul's main pedestrian shopping street, was a suicide bombing gone wrong. In addition to the five deaths, at least 36 people were injured - 12 of them foreign nationals, according to the Ministry of Health.

Two Americans were killed in the blast, the White House announced.

"We are in close touch with Turkish authorities and reaffirm our commitment to work together with Turkey to confront the evil of terrorism," White House National Security Council spokesman Ned Price said in a statement.

Also, the Israeli government stated that at least two Israeli nationals died in the attack.

"It is still unclear, whether the attack targeted Israelis," said Prime Minister Benjamin Netanyahu.

The German foreign ministry has called for German tourists to stay indoors.

Helicopters circled overhead as police quickly cordoned off the main entrances and side exits of Istiklal Street, while the smell of the explosion hung in the air long after the attack.

According to officers at the scene, an unknown attacker detonated an explosive device on the corner of Istiklal and Balo sokak, a side street next to the office of the district governor.

"We heard the explosion and then the police came and closed the road - it was frightening of course," said Jacob, the manager of a kebab restaurant on Istiklal Street, just down from the site of the attack.

"Many thousands of people depend for their livelihoods on the commerce of this street," he told DW.

"These attacks just keep happening and we should not be surprised," he continued. "The army is fighting a war in the southeast of the country, and it is obviously making a lot of people angry.

"They have to pull back and stop this: violence is just causing more violence."

At present, no group has claimed responsibility for the explosion.

'They want to scare Turkey'

The attack came just a week after Turkey's capital, Ankara, was struck by large-scale attack that killed 37 people and was subsequently claimed by the Kurdistan Freedom Falcons (TAK), a radical militant group that split off from the banned Kurdistan Workers' Party (PKK) in 2006.

The group claimed the Ankara attack was a response to the government's military operations in the predominantly Kurdish southeast, and warned of future attacks.

"They want to scare Turkey with these attacks [...] they can do whatever they want, but we will not get used to terror," Numan Kurtulmus, Turkey's deputy prime minister, said Saturday after the Istanbul attack.

"Much rides on who is definitively blamed for this bombing," said Aaron Stein, senior resident fellow at the Atlantic Council's Rafik Hariri Center for the Middle East and the author of "Turkey's New Foreign Policy."

Although the perpetrator of the attack has yet to be confirmed, one of the names circulating in the Turkish press is that of Savas Yildiz, a militant linked to the Raqqa-based "Islamic State" group.

"If the bomber is Savas Yildiz, this will simply be the latest in a string of 'Islamic State' attacks in Turkey dating back to May 2015," Stein told DW.

"The reported bomber is accused of having a hand in the first 'Islamic State' attack in Turkey, the twin bombing of [opposition pro-Kurdish party] HDP offices in Adana and Mersin in May."

"But most counterterrorism experts also expected a TAK attack this weekend, so it all depends on the official ID of the bomber."

High likelihood of attacks

In a secret document circulated to municipal workers in Istanbul, and seen by DW, the Istanbul Security Directorate warned of a high likelihood of attacks over the weekend and around the period of Newroz, the Kurdish spring festival, which falls on March 21. Kurds in Turkey have traditionally used the day to assert national identity.

On Thursday, the German embassy in Ankara and consulate in Istanbul, along with the German school in Istanbul, were temporarily closed after German Foreign Minister Frank-Walter Steinmeier announced that the government had received intelligence of a possible attack. The German school in Istanbul is located on a side road off Istiklal Street.

(Reuters, AFP, AP)