A Turkish member of the Islamic State militant group was responsible for the suicide bombing in Istanbul that killed three Israelis and an Iranian, Turkey's interior minister says.
The attack in Istiklal Street, Istanbul's most popular shopping distict, is the fourth such bombing in Turkey this year and the second one by Islamist militants. In January a suicide bomber blew himself up in Istanbul's historic heart, killing 12 German tourists.
NATO-member Turkey is on heightened alert after the bombings, which have killed more than 80 people. A soccer match between Istanbul rivals Fenerbahce and Galatasaray was cancelled on Sunday and the stadium evacuated on what appeared to be a security threat.
Interior Minister Efkan Ala identified Saturday's bomber as a man from a southern Turkish province, adding that five people had been detained so far in connection with the blast.
"We have determined that Mehmet Ozturk, born in 1992 in Gaziantep, has carried out the heinous attack on Saturday in Istanbul. It has been established that he is a member of Daesh," Ala told a news conference broadcast live on television, using an Arabic acronym for Islamic State.
Israel has confirmed that three of its citizens died in the blast. Two of them held dual citizenship with the United States.
An Iranian was also killed, Turkish officials have said.
Israeli Prime Minister Benjamin Netanyahu has said Israel is trying to determine whether its citizens were deliberately targeted. Eleven of the 36 wounded were Israelis.
In his first public appearance since the bombing, President Tayyip Erdogan said Turkey would not give in to militants.
"We will never surrender to the agenda of terror. We will defeat the terrorist organisations and the powers behind them by looking after the unity of our nation," he said.
As part of a US-led coalition, Turkey is fighting Islamic State in neighbouring Syria and Iraq. It is also battling Kurdish militants in its southeast, where a ceasefire collapsed last July, triggering the worst violence since the 1990s.
An offshoot of the militant Kurdistan Workers Party (PKK) claimed responsibility for two recent car bomb attacks in the capital Ankara that killed a total of 66 people.
Police were questioning the father and brother of the alleged bomber Ozturk and had determined his identity by checking a DNA sample from the blast scene against one taken from his father, security sources said.
Ozturk's family reported him missing after he went to Istanbul in 2013, the security sources said.
Police were on also on alert due to concerns about potential clashes between security forces and Kurdish militants during a spring festival this weekend that is widely celebrated by Kurds.
Interior Minister Ala said authorities had put 200,000 members of the police and gendarmerie on duty, some of whom would set up checkpoints. Hundreds of bomb control devices had also been dispatched.
