President Vladimir Putin on Wednesday sternly warned the West against further encroachment on Russia’s security interests, saying Moscow’s response will be “quick and tough.”

Putin’s warning during his annual state-of-the-nation address came amid a massive Russian military buildup near Ukraine, where cease-fire violations in the seven-year conflict between Russia-backed separatists and Ukrainian forces have escalated in recent weeks. The United States and its allies have urged the Kremlin to pull the troops back.

“I hope that no one dares to cross the red line in respect to Russia, and we will determine where it is in each specific case,” Putin said. “Those who organize any provocations threatening the core security interests of Russia will feel sorry for their deeds as never before.”

Moscow has rejected Ukrainian and Western concerns about the troop buildup, saying it doesn’t threaten anyone and Russia is free to deploy its forces on its territory. But the Kremlin also has warned Ukrainian authorities against trying to use force to retake control of the rebel-held east, saying that Russia could be forced to intervene to protect civilians in the region.

“We really don’t want to burn the bridges,” Putin said. “But if some mistake our good intentions for indifference or weakness and intend to burn or even blow up those bridges themselves, Russia’s response will be asymmetrical, quick and tough.”

Putin pointed to Russia’s moves to modernize its nuclear arsenals and said the military would continue to procure a growing number of state-of-the-art hypersonic missiles and other new weapons. He added that development of the nuclear-armed Poseidon underwater drone and the Burevestnik nuclear-powered cruise missile is continuing successfully.