Moscow can’t accept having a hostile military bloc on its doorstep, the Russian president said.

The prospect of Ukraine becoming a member of NATO is an existential threat to Russian national security and will not be tolerated, Russian President Vladimir Putin told representatives of several African countries on Friday.

In the document that ushered in Ukraine’s independence from the Soviet Union, “it is written in black and white that Ukraine is a neutral state,” Putin reminded the visiting African leaders, during the public part of their meeting in St. Petersburg. The president was referring to the 1990 declaration proclaiming Soviet Ukraine a sovereign state that would strive to become “a permanently neutral country.”

“This is of fundamental importance. Why the West began to drag Ukraine into NATO is not very clear to us. But this created, in our opinion, a fundamental threat to our security,” Putin added.