ISTANBUL, Turkey—One man was killed after gunmen opened fire inside a Catholic church in Istanbul during Sunday mass in what appeared to be a targetted attack.

The shooting, condemned by Pope Francis and Turkish officials, was claimed by the so-called Islamic State group in a statement issued on its Telegram channels.

Two masked men carried out the attack at around 11:40 am (0840 GMT) at the Santa Maria church in the Sariyer district, on the European side of Turkey's largest city, Interior Minister Ali Yerlikaya said on social media.

Turkish officials said it looked like a targeted attack against one person rather than against the Catholic church.

The minister said an individual initially identified only as C.T. was the target of the gun attack and had lost his life. He was among those attending Sunday's service.

Turkish police detained the two suspects as they fled the scene, Yerlikaya announced late on Sunday, identifying the victim as Tuncer Cihan.

Istanbul governor Davut Gul said there had been no other injuries.

Local officials said around 40 people attended the mass including Poland's consul general in Istanbul Witold Lesniak and his family.

They also suggested that, but for a weapons malfunction, there might have been more casualties.

"After the second shot, the gun didn't work, then they (the attackers) ran," Sariyer district's mayor Sukru Genc told reporters.

"At this moment, everyone lay on the floor. There were around 35 to 40 people inside."

The Polish foreign ministry didn't comment on the diplomat's presence, saying only it was "monitoring the situation".

-'Closeness to community'-

Television images showed police and an ambulance outside the ornate 19th-century church.

Security footage from before the attack showed a pair of men wearing black ski masks with their hands hidden in their pockets. One was wearing sunglasses.

President Recep Tayyip Erdogan, who was in the central Anatolian province of Eskisehir for his party's rally ahead of March local elections, expressed condolences during a phone call with the priest of the Italian church and other local officials.

The "necessary steps are being taken to catch the perpetrators as soon as possible", he said, according to his office.

Pope Francis expressed his support for the Catholic church after the attack, in comments at the end of his weekly Angelus prayer in St Peter's Square at the Vatican.

Italy's Foreign Minister Antonio Tajani also expressed his "condolences and firm condemnation" over the attack, and backed the Turkish authorities to find the killers.

- Widespread condemnation -

The incident comes more than a week after Italian Prime Minister Giorgia Meloni met Erdogan in Istanbul.

Turkey's ruling AKP party spokesman Omer Celik said the attackers took aim at a citizen during the mass.

"Our security forces are conducting a large-scale investigation into the matter," he said. "Those who threaten the peace and security of our citizens will never achieve their goals."

Istanbul's popular mayor Ekrem Imamoglu said: "We will never allow those who aim at our unity and peace by attacking houses of religion in our city."

In December last year, Turkish security forces detained 32 suspects over alleged links with the IS group who were planning attacks on churches and synagogues, as well as the Iraqi embassy.

IS extremists have carried out a string of attacks on Turkish soil, including against a nightclub in Istanbul in 2017 that left 39 people dead.

In its statement Sunday, the IS said the attack had been carried out in response to the group leader's call to kill Jews and Christians everywhere.