Dutch Defence Minister Ank Bijleveld on Thursday said the Netherlands has expelled four Russian agents who allegedly targeted the computer networks of the Organisation for the Prevention of Chemical Weapons in The Hague in April, AFP reported. Dutch intelligence services thwarted the cyber attack by Russian GRU military intelligence agency, the minister added.

Bijleveld said Dutch investigators discovered that the Russian agents had also targeted the MH17 plane crash investigation files. In May, Dutch investigators claimed a Russian missile had brought down Malaysia Airlines flight over Ukraine in 2014.

The Russian agents reportedly used a car full of electronic equipment that was parked close to the offices of the global chemical weapons watchdog to hack into their computer system, the Dutch official said. Major-General Onno Eichelsheim of the MIVD intelligence service said the operatives were in the country on Russian diplomatic passports.

At the time of the hacking attempt, the international watchdog was investigating the poisoning of former Russian spy Sergei Skripal and his daughter in Salisbury, United Kingdom, using a nerve agent. Dutch investigators also found a laptop that had information on the investigation into the 2014 shooting down of flight MH17.

“The Dutch government finds the involvement of these intelligence operatives extremely worrisome,” Bijleveld said. “Normally we don’t reveal this type of counter-intelligence operation.”