Russia on Thursday claimed Ukraine was ramping up efforts to invade Transnistria, Moldova's Moscow-backed separatist region, and pledged a "response."
The Russian defence ministry's statement was released on the eve of the one-year anniversary of Moscow's offensive in Ukraine.
Since the launch of the full-scale assault against Ukraine a year ago, the Kremlin has been accused of raising tensions in Transnistria to destabilise Ukraine and Moldova.
"The Kyiv regime has stepped up preparations for the invasion of the Transnistrian Moldavian Republic," the statement said.
The defence ministry claimed the "invasion" would be launched "in response to an alleged offensive by Russian troops from the territory of Transnistria."
The Russian Defense Ministry claimed that Ukrainian troops were massing at the border with Moldova's breakaway region.
"The implementation of the planned provocation by the Ukrainian authorities poses a direct threat to the Russian peacekeeping contingent legally deployed in Transnistria," Moscow said.
"Russia's armed forces will respond to the impending provocation of the Ukrainian side in an adequate manner," the statement added.
The government of Moldova said Thursday that "state authorities do not confirm the information released this morning by the Russian Defense Ministry."
"We call for calm and to obtain information from official and trusted sources of the Republic of Moldova," it said on its Telegram channel.
Earlier this month, Moldovan President Maia Sandu accused Russia of plotting to violently overthrow her government through saboteurs disguised as anti-government protesters, claims that Russia denied.
Transnistria is a narrow region bordering Ukraine, which separated from Moldova after a short war in 1992. Russian soldiers have been deployed there since.
Moldova, a poor country of 2.6 million people with a sizeable Russian minority, has taken a pro-Western turn in recent years, angering Moscow.