BRUSSELS (AP) — NATO Secretary-General Jens Stoltenberg said Thursday that the organization withdrew the accreditation of eight Russian officials to the military alliance in response to a rise in “malign activities” by Moscow.

The eight officials are to be deprived of access to NATO’s Brussels headquarters from the end of the month because it believes they have been secretly working as intelligence officers. NATO also reduced the number of positions that Russia can accredit people for from 20 down to 10.

“This decision is not linked to any particular event, but we have seen over some time now an increase in Russian malign activity, and therefore we need to be vigilant,” Stoltenberg told reporters.

“The relationship between NATO and Russia is at its lowest point since the end of the Cold War. That’s because of the Russian behavior. We have seen their aggressive actions, not least against Ukraine, but also the significant military buildup and violations of important arms control agreements,” he said.

Stoltenberg said that the decision to withdraw the accreditation of the eight “was done based on intelligence, was done because these are undeclared Russian intelligence officers.” He said NATO must act when Russian delegation members “conduct activities which not in line with their accreditation.”

The Russian mission isn't based at NATO’s headquarters, but in a leafy neighborhood in the south of the Belgian capital, Brussels.

NATO suspended practical cooperation with Russia in 2014 after it annexed Ukraine’s Crimean Peninsula, but has kept channels open for high-level meetings and for military-to-military cooperation. But the NATO-Russia Council, their preferred forum, has only met sporadically since then.

Agreeing on the agenda for NRC meetings has proven a challenge. NATO invited Russia to take part in one such meeting more than 18 months ago, but Stoltenberg said Moscow has declined to take up the offer.