Russia and Belarus signed a deal on Thursday formalising the procedure for deploying Russian nuclear weapons on Belarusian territory. Control of the weapons will remain with Moscow.

The move formalised the deal agreed on earlier by Russian President Vladimir Putin and Belarusian President Alexander Lukashenko.

Putin previously announced in March that his country planned to deploy tactical, comparatively short-range and small-yield nuclear weapons in Belarus. The inking of the deal comes as Russia braces for Ukraine’s much-anticipated counteroffensive. Both Russian and Belarusian officials framed the step as driven by hostility from the West.

“Deployment of nonstrategic nuclear weapons is an effective response to the aggressive policy of countries unfriendly to us,” Belarusian Defence Minister Viktor Khrenin said in Minsk during a meeting with his Russian counterpart, Sergei Shoigu.

“In the context of an extremely sharp escalation of threats on the western borders of Russia and Belarus, a decision was made to take countermeasures in the military-nuclear sphere,” Shoigu added.

Belarus’s Ministry of Defence said the agreement refers to a “special storage facility on the territory of the Republic of Belarus.”

No detail was announced regarding when the weapons would be deployed in Belarus, but Putin previously said that the construction of storage facilities for tactical nuclear weapons in Belarus would be completed by July 1.

Exiled Belarusian opposition leader Sviatlana Tsikhanouskaya condemned the move.