Russian President Vladimir Putin has expressed his strong opposition to the expansion of the North Atlantic Treaty Organization (NATO) eastward, warning the US-led military alliance against unspecified consequences in case it seeks to forge closer ties with Ukraine and Georgia.

Addressing a meeting of Russian ambassadors and envoys in Moscow on Thursday, Putin said there was a need to rebuild trust in Europe, and that NATO's attempts concerning deployment of military contingents and infrastructure near Russia’s western frontiers were not acceptable.

“We will respond appropriately to such aggressive steps, which pose a direct threat to Russia,” the Russian leader said.

He added, “Our colleagues, who are trying to aggravate the situation, seeking to include, among others, Ukraine and Georgia in the orbit of the alliance, should think about the possible consequences of such an irresponsible policy.”

Putin said he had discussed the matter with his US counterpart Donald Trump at a summit in the Finnish capital of Helsinki on Monday.

Russia and Georgia fought a war in August 2008 over the breakaway Georgian region of South Ossetia. Moscow continues to garrison troops there and to support another breakaway region, Abkhazia.

The strategic Black Sea peninsula of Crimea declared independence from Ukraine on March 17, 2014 and formally applied to become part of Russia following a referendum, in which 96.8 percent of participants voted in favor of the move.

After Crimea rejoined Russia, an armed conflict broke out in eastern Ukraine when Kiev launched military operations to quell pro-Russia sentiments there. Kiev accuses Moscow of involvement in the conflict. Russia, in return, has denied the charge.

The US and its Western allies have imposed several rounds of sanctions against Russia over its reunification with Crimea and the Ukrainian crisis, which has killed about 10,000 people since it began in 2014.

Earlier this year, a senior member of the Italian Five Star Movement (M5S) and vice president of the European Parliament told Russia’s Sputnik news agency that the presence of NATO troops close to Russia’s borders contributes to an arms race, and maintains an atmosphere of mistrust between Moscow and the alliance.

Massimo Castaldo also called for the easing of tensions between NATO and Moscow.

“I think that we should bet on the gradual easing of tension, including with the help of signals that we send as NATO, hoping to restore useful and constructive relations [with Russia],” Castaldo pointed out.