A man places carnations at the scene of Saturday’s suicide bombing at Istiklal Street, a major shopping and tourist district, in central Istanbul. (Osman Orsal/Reuters)

Authorities in Turkey on Sunday named a Turkish man with alleged ties to the Islamic State as responsible for the weekend suicide bombing in Istanbul that killed four foreign tourists and deepened fears of rising instability in the country.

The attack on Saturday on Istiklal Street, a major thoroughfare that is one of Istanbul’s biggest draws for tourists and locals alike, underscored the extent to which Turkey is confronting an accelerating threat from extremists on two fronts.

It was the sixth major suicide bombing in Turkey in eight months and came less than a week after an attack claimed by Kurdish militants in the capital, Ankara, killed 37 people, also in a busy shopping district.

As security forces went on heightened alert across the country, which is marking a public holiday, a big soccer tournament in Istanbul was postponed. CNN Turk quoted the Istanbul governor’s office as saying that “serious intelligence” indicated the likelihood of an attack on the match between the Fenerbahce and Galatasaray teams.

“The question, unfortunately, is not if there will be a terror attack again, but when the next attack will be,” said Soner Cagaptay of the Washington Institute for Near East Policy. “To me, this looks like Turkey walking slow motion into disaster.”

A man looks out of a window of a traditional “doner” restaurant, at the site of Saturday's suicide bombing, in Istanbul on Sunday. (Emrah Gurel/AP)

The victims of Saturday’s suicide bombing have been identified as an Iranian and three Israelis, two of whom also held American citizenship, according to Turkish officials and the White House.

At least two dozen people were injured, most of them foreign tourists from Germany, Iceland and Ireland, among other countries.

Turkish authorities named the bomber, who also died, as Mehmet Turk, born in 1992, from the southern city of Gaziantep near the border with Syria. The suspect’s identity was confirmed through DNA tests performed on his remains and his relatives, authorities said.

“Current findings show that the terrorist has links to the Daesh terror organization,” Interior Minister Efkan Ala told reporters in Ankara, using the Arabic acronym for the Islamic State militant group.

Turk was already wanted on suspicion of links to the Islamic State, and his relatives, who believed he had vanished in Syria, identified him from security camera footage broadcast on Turkish television, according to local media reports.

The bodies of the three Israeli victims were flown home to Israel on Sunday. Israeli media quoted Israeli officials as saying there was no reason to believe Israelis had been singled out in the attack.

People walk on Istiklal Street near the site of Saturday’s suicide bombing in Istanbul. (Emrah Gurel/AP)

The string of attacks in recent months has illustrated the extent to which Turkey’s entanglement in two conflicts is spilling over into its cities, threatening the economy and destabilizing the country.

One campaign is being waged with its restive Kurdish population in the southeast, where thousands of people have been displaced and hundreds killed since a cease-fire collapsed last summer.

The other is in Syria, where Turkey has supported rebel groups battling President Bashar al-Assad in an effort that has opened the door to the emergence and strengthening of extremist organizations such as the Islamic State.

There was no claim of responsibility for the Istiklal bombing, the second suspected Islamic State attack on foreign tourists in Istanbul this year and the fourth in Turkey since July. In January, a suicide bomber identified by the authorities as a Syrian Islamic State member killed 12 German tourists in the city’s historic Sultanahmet district.

Meanwhile, a shadowy Kurdish group called TAK, or Kurdistan Freedom Falcons, has asserted responsibility for two suicide attacks in Ankara, including the one on March 13. The little-known group is thought to be an offshoot of the PKK, or the Kurdistan Workers’ Party, a group designated as a terrorist organization by Turkey and the United States.

Ruth Eglash contributed from Jerusalem.

Read more:

Turkey targets U.S.-backed Kurds in Syria

Turkish envoy: Washington making ‘strategic mistake’ to back Syrian Kurds

Turkey sees enemies and worries in all directions

Today's coverage from Post correspondents around the world