Dutch authorities disrupted an attempt in April by Russian intelligence agents to hack the Organization for the Prohibition of Chemical Weapons, Defence Minister Ank Bijleveld said.

At a press conference in the Hague, Bijleveld called on Russia to cease its cyber activities aimed at "undermining" Western democracies.

According to a presentation by the head of the Netherlands' military intelligence agency, four Russians arrived in the Netherlands on April 10 and were caught with spying equipment at a hotel located next to the OPCW headquarters.

At the time, the OPCW was working to verify the identity of the substance used in the March attack in Salisbury, Britain, on former Russian spy Sergei Skripal and his daughter Julia. It was also seeking to verify the identity of a substance used in an attack in Douma, Syria.

The four Russians in the Netherlands were detained on April 13 and expelled to Russia, Dutch Major General Onno Eichelsheim said. They had planned to travel on to a laboratory in Spiez, Switzerland used by the OPCW to analyse chemical weapons samples, he said.

Russian military intelligence "is active here in the Netherlands ... where a lot of international organisations are" based, Eichelsheim said.