KYIV, Feb 19 (Reuters) - Reports that Ukraine has been shelling regions controlled by Moscow-backed separatists and inside the Russian border are "pure lies", Ukraine's president said on Saturday, adding that his country would not respond to provocations.

President Voldymyr Zelenskiy was addressing senior Western security officials at the annual Munich Security Conference amid reports of explosions inside Russian territory to Ukraine's east, and in breakaway regions of Ukraine.

"What was shown yesterday in the temporarily occupied territories, some shells allegedly flying from our side, some flying all the way to Rostov, these are pure lies," he said. "They are blowing up something on their side."

He urged Western countries not to wait for a possible Russian invasion to impose sanctions on Russia.

Russia, which has massed some 150,000 troops along Ukraine's eastern borders, has said that for its own long-term security it needs a commitment that Kyiv will never join the NATO military alliance.

But leaders of Western countries, which believe Russia is preparing a possible invasion of Ukraine, said Russia would face severe consequences if it attacked, warning Moscow against attempts to redraw Europe's borders.

"National borders should not be changed by force," U.S. Vice President Kamala Harris said.

"We have prepared economic measures that will be swift, severe, and united," she said. "We will target Russia's financial institutions and key industries."

Both Ukraine and NATO members have refused to rule out Kyiv one day joining the alliance, though few expect that soon.

But, referring to an explosion at a kindergarten in the occupied east, Zelenskiy urged delegates not to let the rhetoric obscure the plight of ordinary people.

"Those kids aren't heading towards NATO. They are heading to their classrooms," he said.