Live updates: follow the latest news on Russia-Ukraine
Moldova, like Ukraine, is a former Soviet Union satellite with a breakaway Russia-allied region in its east.
In Ukraine, that breakaway region is at the centre of Russian battle plans after years of Moscow-allied rebels fighting. In Moldova, it is friends with Russia along part of the border with Ukraine.
What is Transnistria?
It is a region that broke away from Moldova as the USSR collapsed into separate states after the Cold War.
Transnistria used to be part of a Russian-speaking area of Ukraine, while the rest of Moldova has Romanian heritage. Ethnic Russians and Ukrainians outnumber ethnic Moldovans.
Its statehood is not internationally recognised, but Russia has been its prime supporter.
It has a population of about 469,000 people.
Where is it?
It is a sliver of land of about 4,100 square kilometres between the Dniester River and the Ukraine border. Moldova is 33,800 km2.
How did it come about?
Transnistria declared independence from West-leaning Moldova in 1990. After a short war in 1992, which killed hundreds of people, a ceasefire was signed.
During the war, the Russian army, which still has forces in Transnistria, backed the rebels in a way similar to Russia’s presence in eastern Ukraine.
A referendum in 2006, that was not internationally recognised, found 97.1 per cent of voters wanted to join Russia.
Who controls it?
The territory has seen de facto independence since 1992, but that is not internationally recognised.
Its government and economy are heavily dependent on subsidies from Russia, which keeps an influential role.
Russia also has a military presence and peacekeeping mission in the territory.
There is little in the way of political competition or independent media.
What has happened?
The Moscow-backed Transnistria interior ministry said on Wednesday that shots were fired at a village housing a Russian arms depot after drones flew from Ukraine.
Kolbasna, about 2km from the Ukrainian border, houses a stockpile of 20,000 tonnes of munitions dating back to the Soviet era, which are guarded by Russian troops.
There have also been reports of explosions after what the administration called “terrorist attacks” .
Ukraine has raised concerns that the land could be used by Russian forces in a way similar to how it has used Belarus during the Ukraine war.