The presidents of Russia and Belarus had already discussed a plan to put nuclear weapons on NATO's doorstep. Now, Vladimir Putin and Alexander Lukashenko say they will work more closely together on trade and defense.
The leaders and their senior officials held a meeting in Moscow on Thursday.
Putin announced last month that he wants to move some tactical nuclear arms to Belarus. The hope is that the deployment might discourage members of the alliance from supporting Ukraine.
Putin said, "Naturally, it's worth working substantively on strategic plans. We will further strengthen the security of the Union State to guarantee sustainable and progressive social and economic development."
Lukashenko has seen Western leaders try to exert economic pressure on Russia and Belarus via sanctions. He said their failure to do so has led them to try another tactic.
Lukashenko said, "They've started putting military pressure on us. They've built up NATO forces along the borders of Russia and Belarus."
Putin has said he wants storage facilities for the nuclear arms to be completed by July. However, Belarusian officials say they still have 43 weapons facilities across the country that were set up during the Soviet era.