Heavily armed police are protecting churches across Istanbul day and night after an Islamic State attack on a Catholic church in Istanbul. The terrorist group has warned of further attacks against Christians and Jews.

Turkish security forces have detained hundreds of suspects in the aftermath of January's deadly attack on Santa Maria Catholic Church in the Sariyer district, which killed one person.

The death toll could have been considerably higher if the gunmen's automatic weapons had not jammed.

The Islamic State group claimed responsibility in a statement that warned it was targeting Jews and Christians in Turkey. 

Istanbul's small Christian community, although fearful, remains defiant.

"It's not necessary to be a member of the congregation to be frightened. It's something that would terrify anyone," declared Ilhan Guzelis after attending his local church service.

"We're scared, but believe me, we've never hesitated to come to our church, to worship here, and to pray to God."

Game of cat and mouse

Two men, a Russian and a Tajik national, have been arrested for carrying out the attack, while over a hundred others have been detained across the country.  

Experts say Turkish security forces are now engaged in a deadly cat-and-mouse game with the terror group also known as Isis or Daesh. 

"This is a mutual competition between the security forces and terrorist cells," Murat Aslan of the Ankara-based Foundation for Political, Economic and Social Research (Seta) told RFI.

"Both sides will try to identify or deceive each other. And in this case, I believe the Daesh terrorists were skilful, at least to bypass the security measures."

Aslan warns the job is becoming harder for Turkey's security forces as the face of Islamic State evolves. He cites changes to assailants' personal appearance, for example: recent attackers have worn regular clothes and shaved their beards, which helps them blend into a crowd.

"They are regular citizens. So it's not that much easier to distinguish exactly who is radical or not, for instance. In the latest incident in the church, the individuals were like regular citizens," he said.

Turkish targets

Adding to security woes is the proximity of Turkey to Syrian territory once held by Islamic State and other radical jihadist groups.

"There are armed groups in Turkey. They still have baggage in Turkey, the remnants of the armed groups inside Turkey, even Isis remnants back from the Syrian war," claims Sezin Oney of the Politikyol news portal.

The last time Islamic State successfully carried out a major attack in Turkey was in 2017, when a gunman went on the rampage during New Year celebrations, killing 39 people at an Istanbul nightclub.

But Aslan warns that Turkey offers numerous targets.

"The church attack was really significant in terms of the potential of Daesh," he says.

"Turkey hosts a lot of churches and Jewish holy sites. Once [terrorists] enjoy a presence here and set up hidden cells, they can easily select a target."

Fears for tourist season

With Turkey's lucrative tourism season only a month or so away, bringing with it further potential targets for Islamic State, the government security crackdown is predicted to intensify.

Christians like Guzelis have mixed feelings over the presence of such patrols around the city's churches.

"After such an incident, it is good for us that [the police] come here to protect us here again, even as a presence; we are grateful for this," he says.

"I wish that there would be no such matters, that everyone would live together here as brothers and sisters. But we are sorry for what happened; it creates a bitterness in us."

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