VLADIMIR PUTIN HAS warned the West against encroachment on Russia’s security interests, saying Moscow’s response will be “quick and tough”.

The president’s warning during his annual state-of-the-nation address came amid a massive Russian military build-up near Ukraine, where ceasefire violations in the seven-year conflict between Russia-backed separatists and Ukrainian forces have escalated in recent weeks.

The US 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 organise 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 build-up, saying it does not threaten anyone and Russia is free to deploy its forces on its territory.

But the Kremlin has warned Ukrainian authorities against trying to use force to retake control of the rebel-held east, saying 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.”

He pointed to Russia’s moves to modernise its nuclear arsenals and said the military would continue to procure 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.

Without singling out a specific country, the Russian leader denounced a foreign government that imposes “unlawful, politically motivated economic sanctions and crude attempts to enforce its will on others”.

He said Russia has shown restraint and often refrained from responding to “openly boorish” actions by others.

The Biden administration last week imposed an array of new sanctions on Russia for interfering in the 2020 US presidential election and for involvement in the SolarWind hack of federal agencies — activities Moscow has denied.

The US ordered 10 Russian diplomats expelled, targeted dozens of companies and individuals, and imposed new curbs on Russia’s ability to borrow money.

Moscow retaliated by ordering 10 US diplomats to leave, blacklisting eight current and former US officials, and tightening requirements for US embassy operations.

“Russia has its own interests, which we will defend in line with the international law,” Putin said.

“If somebody refuses to understand this obvious thing, is reluctant to conduct a dialogue and chooses a selfish and arrogant tone, Russia will always find a way to defend its position.”

Putin dedicated most of his annual address to domestic issues, hailing the nation’s response to the coronavirus pandemic.

He said the quick development of three vaccines underlined Russia’s technological and industrial potential, and called for a quicker pace of immunisations, voicing hope that the country could achieve collective immunity this autumn.

He put forward a range of economic incentives to help the economy recover from the pandemic and new social payments focusing on families with children.

As he spoke, a wave of protests started rolling across Russia’s far east in support of imprisoned opposition leader Alexei Navalny.

The politician, who is Putin’s most persistent critic, started a hunger strike three weeks ago to protest over what he said was inadequate medical treatment for back pain and officials’ refusal to allow his doctor to visit him in prison.