Turkey blamed an Islamic State militant Sunday for the suicide bombing in Istanbul the day before that killed four people and wounded dozens more.
Interior Minister Efkan Ala said the attack was carried out by a Turkish citizen, Mehmet Ozturk, who was born in 1992 in Gaziantep province, which borders Syria.
Ala said the suspected bomber, who also was killed in the attack, was not on Turkey's terrorist watch list.
The Turkish official said five people allegedly linked to the attack have been detained.
Three Israelis, two of them with dual U.S. citizenship, and an Iranian were killed in the blast on Istiklal Street, lined with shops and cafes in an area that also houses government offices and foreign consulates.
A man leaves carnations at the Saturday explosion site in Istanbul, March 20, 2016.
Saturday's explosion was the sixth suicide bombing in Turkey since July, blasts that now have killed more than 200 people, with some of the attacks blamed on Islamic State jihadists and others on Kurdish militants engaged in a three-decade fight for more autonomy in southeastern Turkey.
Ala said Turkey is determined to pursue its fight against Islamic State jihadists, but admitted it was difficult to prevent suicide bombings.
On Sunday, people commemorated those killed in the Istanbul attack, placing carnations and candles at the site of the blast, with one sign that said, "We are on the streets, we are not afraid of you."
It was not immediately clear whether the Israelis were targeted in the attack, but Israeli Prime Minister Benjamin Netanyahu said its intelligence officials were looking into the possibility.
White House spokesman Ned Price said the United States condemns the attack in the strongest possible terms and affirmed U.S. commitment to work with Turkey to "confront the evil of terrorism."