Belarus is not a member of NATO but has had ties with the military alliance since 1992 following the fall of the Soviet Union, and has maintained a diplomatic mission to NATO since 1998.
Belarusian personnel can attend seminars and meetings at NATO and in NATO countries as part of a cooperation partnership that tackles issues such as arms control and military education.
"We have decided to restrict the access of Belarusian personnel to the NATO headquarters," Stoltenberg told a news conference ahead of meetings of NATO defense and foreign ministers on Tuesday, without giving more details.
Asked about new Russian military formations and units, intended to be deployed close to the alliance's borders, Stoltenberg said NATO would continue to seek dialogue with Moscow, while also exercising troops for defensive purposes.
"It is important to manage the difficult relationship with Russia with transparency on military activities, risk reduction and also for instance related issues like arms control," Stoltenberg told reporters.
Russia's ties with the West are acutely strained over the jailing of Kremlin critic Alexei Navalny, a military build-up near Ukraine as well as allegations of election hacking.