The US is going to provide Bulgaria with Stryker mechanized infantry company for its battlegroup under NATO’s drive to bolster its eastern flank, said the Bulgarian Prime Minister Kiril Petkov on Saturday.

“The USA agreed to provide a Stryker company,” he told a press conference with US Defence Secretary Lloyd Austin. “This is a strong sign to all of our allies in NATO.”

“I wanted to underscore the importance of the announcement that Bulgaria has established and is leading a NATO multinational battlegroup. It is an important step and we fully support it,” Austin said.

It comes after Bulgaria’s foreign ministry announced the expulsion of 10 Russian diplomats.

The EU member said they had breached international conventions on diplomatic ties, a formulation often used by the ministry to designate espionage.

Petkov said Bulgaria would continue to send humanitarian aid to Ukraine and take in Ukrainian refugees from the war, but it was not considering sending any weaponry to Kyiv for the time being as his Black Sea country was too close to the conflict.

Bulgaria, once Moscow’s closest ally during the Cold War era but a NATO and European Union member state, is establishing a battlegroup of up to 1,000 troops under the operational command of NATO’s Supreme Allied Commander Europe.

The battlegroup is expected to host troops from other allied countries as well.

Speaking after chairing a NATO summit, Secretary-General Jens Stoltenberg said the 30-nation organization will send parts of the NATO Response Force and elements of a quickly deployable spearhead unit to the alliance’s eastern flank. It’s the first time the force has been used to defend NATO allies.

In response to Europe’s biggest security crisis in decades, Stoltenberg said, “We are now deploying the NATO Response Force for the first time in a collective defense context. We speak about thousands of troops. We speak about air and maritime capabilities.”

“There must be no space for miscalculation or misunderstanding. We will do what it takes to protect and defend every ally, and every inch of NATO territory,” he said.

The NRF can number up to 40,000 troops, but Stoltenberg said that NATO would not be deploying the entire force. Parts of a spearhead unit known in NATO jargon as the Very High Readiness Joint Task Force, which is currently led by France, will also be sent.

The announcement came after NATO members, ranging from Russia’s neighbor Estonia in the north down around the west of conflict-hit Ukraine to Bulgaria on the Black Sea coast, triggered urgent consultations Thursday about their security amid concerns from the invasion.