Christian minority
The attack follows the murder earlier this year of Hrant Dink, an Armenian-Turkish editor, by an ultra-nationalist.
Dink's killing prompted extra security measures to be taken for writers and journalists.
The government and other officials in largely Muslim Turkey have in the past criticised Christian missionary work in the country.
The European Union (EU), which Turkey hopes to join, has appealed for more freedom for the Turkey's Christian minority, which comprises less than 1 per cent of the population.
However, some Turkish nationalists see Christian missionaries as enemies of Turkey working to undermine its political and religious institutions.