KYIV, Feb 1 - UK Prime Minister Boris Johnson on Tuesday accused Russian President Vladimir Putin of effectively "holding a gun... to the head of Ukraine" and he called on the Kremlin to step back from a "military disaster,” BBC reported.

Speaking after talks with President Volodymyr Zelensky in Kyiv, Johnson told reporters the Ukrainian army would fight back in the event of an invasion.

"There are 200,000 men and women under arms in Ukraine," he said. "They will put up a very, very fierce and bloody resistance and I think that parents, mothers, in Russia, should reflect on that fact. And I hope very much that President Putin steps back from the path of conflict and that we engage in dialogue."

Johnson warned that the UK would respond to Russian aggression with a "package of sanctions and other measures to be enacted the moment the first Russian toecap crosses further into Ukrainian territory".

The UK has announced it is giving £88m ($119) to Ukraine to promote stable governance and energy independence from Russia.

Zelensky called for sanctions to be introduced before any escalation, saying he would support any move by the UK to deal with "dirty money" allegedly linked to the Kremlin being laundered through the City of London.

Meanwhile, Putin, in his first significant comments on the crisis in several weeks, accused the US of trying to draw his country into a war in Ukraine, adding that America's goal was to use a confrontation as a pretext to impose more sanctions on Russia.

"It seems to me that the United States is not so much concerned about the security of Ukraine... but its main task is to contain Russia's development. In this sense Ukraine itself is just a tool to reach this goal,” Putin said.

Putin said the US had ignored Moscow's concerns in its response to Russian demands for legally binding security guarantees, including a block on NATO's further expansion to the east.

He suggested that if Ukraine were granted its wish to join NATO, it could drag the other members into a war with Russia.

"Imagine that Ukraine is a NATO member and a military operation [to regain Crimea] begins," the Russian leader said. "What - are we going to fight with NATO? Has anyone thought about this? It seems like they haven't." (bbc/ez)