NATO chief Jens Stoltenberg on Thursday welcomed Russian reassurances about a major upcoming military exercise that has deeply worried the allies, but warned Moscow must live up to its commitments.
Speaking after a "frank" meeting between Russia's NATO ambassador and envoys from the 28-nation alliance, Stoltenberg said both sides had discussed ways to avoid dangerous misunderstandings over issues such as exercises.
Russia had in particular provided numbers of its soldiers, planes and ships involved in the Zapad ("West") war games in Russia and Belarus in September, Stoltenberg said.
"It was significant that at today’s meeting, we exchanged advance briefings on upcoming exercises," Stoltenberg said, adding that NATO had also briefed on its Trident Javelin exercises.
"I am encouraged by this progress."
But he warned that "from previous experience, we have every reason to believe it may be substantially more troops participating than the officially reported numbers."
Rules for military exercises in Europe known as the Vienna Document set thresholds for the number of troops allowed to take part in exercises before the opposing side is allowed to demand a mandatory inspection.
Exercises involving 13,000 or more troops are subject to mandatory inspections. With exercises involving 9,000 or more soldiers, the other side must be notified.
"We call on Russia to adhere to the Vienna Document," which is negotiated under the Organization for Security and Cooperation in Europe (OSCE), Stoltenberg said.
Many NATO allies, especially those such as the Baltic states and Poland once ruled from Moscow, are deeply suspicious of Russia, fearing a repeat of its intervention in Ukraine under the cover of a military exercise.
They say Russia has carried out exercises involving many more troops -- reports cite figures of up to 100,000 -- but formally splitting them up in such a way as to get around the rules.
Stoltenberg said the Russian officials gave figures but declined to make them public, saying it was up to Moscow to do so.
Stoltenberg said Trident Javelin is in contrast only a "command post" exercise, involving 5,000 personnel in preparation for next year's much larger Trident Juncture manoeuvres with around 30,000 troops.