Istanbul suicide bombing: Deadliest attack on Germans in over 13 years

It was a strike at the heart of Turkey's culture and its multibillion-dollar tourist industry.

The suicide bombing on Sultanahmet Square on Tuesday killed 10 people -- all of them Germans, the German Foreign Ministry confirmed Wednesday.

It was the deadliest attack on Germans abroad in more than 13 years. And Turkey's Prime Minister promised a determined effort to repel the threat.

"We will continue our fight against terrorism with the same resolve and will never take a step back," Prime Minister Ahmet Davutoglu said, according to Turkey's semiofficial news site, Anadolu Agency.

But he added that Istanbul had "become a city of hope today in the rings of fire in the region, to the people of the Middle East, Balkans and Caucasus."

As if to underscore the government's resolve, Turkey detained 68 suspected terrorists in sweeps across seven provinces, Anadolu Agency reported Wednesday.

That included three Russians who were staying at a house in Antalya, according to an account also reported by Russia's state-run Sputnik news.

Another 21 people held in Sanliurfa were "preparing for attacks in Turkey," according to Anadolu Agency. And 16 people -- 15 of them Syrian -- were detained in Ankara for allegedly starting to scout out buildings there.

One of those caught in the security sweep is being held in connection with the Istanbul blast, according to Turkish Interior Minister Efkan Ala.

"The examination and investigation continues in multiple ways and in a very serious manner," Ala said.

 Another Turkish official, speaking to CNN on condition of anonymity, said Turkey -- and the rest of the world -- would never be safe until the situation in Syria is resolved.

"As long as there is a training ground for ISIS on the other side of our border we will continue to have this problem, not only Turkey but Europe and U.S.," the official said. "Turkey remains committed to its calls for an ISIL-free zone, a region free of terrorism across its borders." ISIL is another acronym for ISIS.

The official said Turkey should try to "drive ISIS into the desert. This isn't a result of Turkish foreign policy; it's about what's happening in Syria."