BRUSSELS: NATO defence ministers are expected this week to set in motion a plan that could establish four multinational battlegroups in southeastern Europe in response to Russia’s military build-up in Ukraine, four diplomats said.

Allied ministers meeting on Wednesday and Thursday will decide whether to order their military commanders to draw up plans to deploy battlegroups of some 1,000 troops each to Bulgaria and Romania, and possibly to Slovakia and Hungary.

With NATO meeting as the United States warns of an imminent Russian invasion of Ukraine, diplomats told Reuters that ministers are likely to agree to direct commanders to come up with a detailed plan for the four battlegroups on land.

“There will be a tasking that allows us to escalate but also to de-escalate if Russia pulls back its military,” a senior NATO diplomat said, stressing that any new battlegroups would be on top of recent allied offers by Britain, the United States and others of ships and planes to reinforce NATO’s eastern flank.

U.S. Ambassador to NATO Julianne Smith told reporters that ministers would discuss “additional enhancements” but declined to give more details. NATO Secretary-General Jens Stoltenberg said: “We’re also going to consider a more long-term adjustment of posture, including considering the battlegroup in Romania.”

They spoke as Russia said some troops near Ukraine were returning to their bases after military exercises, easing concerns over a potential invasion. But Stoltenberg also said that while he saw signs for optimism, he had not seen yet seen any sign of de-escalation on the ground.

Ukraine is not a NATO member and the alliance is under no treaty obligation to defend it. Reinforcements in the Black Sea would show resolve in the strategically important region, and in countries such as Hungary and Slovakia that border Ukraine.

Any final decision on deployments would come later on, although both France and Bulgaria have offered to lead the battlegroups in Romania and Bulgaria respectively. With Budapest wary of provoking Russia, Hungary could stand up a battalion entirely of its own troops, under NATO command, diplomats said.

The move would be NATO’s biggest shift in force posture since it set up its “Enhanced Forward Presence” battlegroups in Estonia, Lithuania, Latvia and Poland - backed by tanks, air defences and intelligence and surveillance units - in response to Russia’s annexation of Crimea in 2014.

Any deployments would go against Moscow’s security demands for the alliance to withdraw troops from eastern Europe. But envoys said an increased troop presence of 4,000 troops was not comparable to the estimated 130,000 Russian troops and equipment to the north, east and south of Ukraine.

NATO insists that the battlegroup format used in the Baltics is not a permanent stationing of troops, rather a “persistent” presence of rotating soldiers to serve as a tripwire for a larger response force should Russia invade NATO territory.

A French presidency official said French troops will deploy to Romania only after a NATO decision and that the designing and arming the battlegroups would still take time because allies must come forward to participate. “There will be a debate within the North Atlantic Council and we are basically aiming for a deadline of a few months,” the official said.

NATO could also consider a multinational force led by France in Romania that would coordinate allied exercises in eastern Europe and allow troops to flow in and out of the region without establishing a formal presence.