ISTANBUL, Turkey - The suicide attacker who detonated a bomb that killed 10 German tourists in the heart of Istanbul's historic district had registered as a refugee just a week earlier, Turkish officials said Wednesday, raising questions over whether extremists are posing as asylum-seekers to inflame anti-immigrant sentiment in Europe.

Turkish authorities identified the assailant in Tuesday's attack as a Syrian man who was born in 1988, and said he was affiliated with the Islamic State. Turkish media, including some close to the government, identified him as Nabil Fadli and said he was Saudi-born. The extremist group has not so far claimed the attack.

Meanwhile, Turkish police arrested five people suspected of direct links to the bomb attack, which took place just steps from the historic Blue Mosque in Istanbul's storied Sultanahmet district. The suspects were not identified.

The bomber had recently entered Turkey, authorities said, and Interior Minister Efkan Ala confirmed reports he had registered with an Istanbul branch of the Migration Management Authority, providing fingerprints that allowed officials to quickly identify him. Ala said the bomber wasn't on any Turkish or international watch lists for IS militants.

"This person was not someone who was being monitored," Prime Minister Ahmet Davutoglu said. "It is a person who entered normally, as a refugee, as an asylum-seeker."

The attack wounded 15 people, including nine Germans and citizens of Norway, Peru and South Korea. Six of the victims remained hospitalized on Wednesday.

Although not as deadly as two attacks in Turkey last year that were blamed on IS, Tuesday's bombing had heightened resonance because it struck at Turkey's $30 billion tourism industry, which has already suffered from a steep decline in Russian visitors since Turkey shot down a Russian warplane near the Syrian border in November.

The fact that the bomber had registered as a Syrian refugee suggests central planning by Islamic State leaders, either to cover their tracks or provoke a backlash in Europe against legitimate Syrian asylum-seekers, said Firas Abi-Ali, an analyst with the security consultancy IHS Country Risk.