Singapore has deported eight Indonesians due to security concerns , the Ministry of Home Affairs said on Thursday, as the island nation heightens its alert against potential Islamist militants.

The Indonesians, aged between 16 and 37, were deported on Tuesday after Singapore authorities found that one of them possessed images of Islamic State fighters and of a shoe bomb, the ministry said.

The eight were deported to Malaysia, the ministry said. It was not immediately clear why they were sent to Malaysia and the ministry was not immediately available for comment.

In December, Singapore said that it had deported the majority of about 70 foreigners it had investigated for suspected radicalism in the past two years, although none planned to carry out attacks in the city state.