The terror attack occurred at around 11:40 (0840 GMT) at the Santa Maria church in the Sariyer district of Istanbul on the European side and was carried out by two masked men, Interior Minister Ali Yerlikaya said on social media.

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

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

An investigation had been launched to find the attackers, Yerlikaya added, who fled the scene after the shooting.

Local officials said around 40 people attended the mass.