NATO must be aware that pushing further into Eastern Europe, past Moscow’s declared red lines, will make a military response inevitable, a top Russian diplomat has warned, amid escalating tensions with the US-led bloc.

Speaking to Rossiya 24 TV on Monday, Konstantin Gavrilov, the head of the Russian delegation to the Negotiations on Military Security and Arms Control in Vienna said Washington was obliged to engage in a dialogue with Moscow on security guarantees for the sake of peace on the continent, whether officials wanted it or not.

“The conversation must be serious, and everyone in NATO is well aware, despite all the power and strength, that it is necessary to take concrete political actions, otherwise the alternative is a … military response from Russia,” he explained.

Gavrilov’s comments came shortly after Moscow issued two documents, one for NATO and the other for US officials, requesting a wide range of assurances it said were aimed at enhancing the security of all parties.

The proposal to NATO focuses mainly on the movement of personnel and hardware, and includes the requirement that Kiev’s long-held ambition to join the bloc would not be realized. A separate clause calls for the current members to renounce any military activity on the territory of Ukraine, as well as in Eastern Europe, the South Caucasus, and Central Asia.

In its proposition to Washington, Moscow requested that officials commit to ruling out expansion into former Soviet republics. Concerns over the US-led military bloc’s potential widening into Eastern Europe have been reignited in recent weeks. Speaking via video link earlier this month, Russian President Vladimir Putin told his US counterpart, Joe Biden, his country was “seriously interested” in getting “reliable and firm legal guarantees” that would prohibit NATO’s expansion further eastwards, as well as the deployment of “offensive strike weapons systems” nearby.

Foreign Ministry spokeswoman Maria Zakharova warned at the beginning of December that further enlargement of the bloc in the direction of Russia was a red line for Moscow, and that Ukraine’s hopes of joining its ranks were unacceptable. The US was pulling Kiev into the orbit of NATO and turning it into a “bridgehead” of confrontation with Russia, she said, in a move that could destabilize Europe.