Between 15 and 20 former members of the Dutch armed forces are now fighting in Syria and Iraq, mainly for anti-Isis militias, the MIVD security service said on Wednesday.

Most have joined Kurdish and Christian armed groups but one is thought to have joined an extreme Islamic group, the security service said in its annual report. ‘In 2015, the defence ministry was confronted for the first time by the case of an active recruit who has… probably joined Isis,’ the report says.

Last September it emerged that a 26-year-old air force sergeant had probably left the Netherlands to join Islamic militants in Iraq or Syria.

Some of the soldiers who have travelled abroad have seen active service. In January, former solder Jitse Akse was arrested after going public with his support for the Kurdish militia YPG and saying on Facebook he had killed Isis fighters.

Thousands of people signed a petition opposing his arrest. That case is still ongoing.

Dutch nationals who take up arms against IS fall under Dutch criminal law and can be prosecuted if they commit crimes.

Spying

The MIVD also writes about the increased threat posed by digital spying techniques, which, it says, are becoming more aggressive and more advanced.

There is an ‘attempt to spy digitally on Dutch interests on a weekly basis’, the report states. The most important targets are the foreign affairs and defence ministries, it says.