Transdniestria split from Moldova before the 1991 collapse of Soviet rule and fought a brief war against the newly independent country, but it has existed for more than 30 years on the country's eastern fringe with little turmoil.

The two sides hold periodic talks on resolving their differences, but tension has risen in the new year over Moldova's imposition of customs duties that the separatist side says will hurt its businesses. Moldovan officials described the latest session of talks earlier this month as "difficult".

Transdniestria's foreign minister, Vitaly Ignatiev, said he was wary of recent changes to Moldova's criminal code toughening its provisions against separatism. He said he could no longer abide by the principle of alternating the talks between the Moldovan capital, Chisinau, and Tiraspol, the separatist region's main town.

"No resident of Transdniestria can be safe from criminal prosecution if he is on the other side of the Dniester River," Ignatiev said, referring to the government-controlled area of Moldova.

"Within the context of our talks, we have repeatedly asked for guarantees against the use of repressive measures against citizens of Transdniestria. But Chisinau won't provide them."

Given the new criminal provisions, he said, talks could only be held either in Transdniestria or by video conference.

The pro-European government in Moldova, one of Europe's poorest countries and which lies between Ukraine and Romania, has pledged to press on with a drive to join the European Union.

President Maia Sandu has denounced Russia's invasion of Ukraine and accused Russia of plotting to remove her. She says Moldova could join the EU initially without Transdniestria, citing membership granted to the divided island of Cyprus.

Moldova's chief negotiator, Deputy Prime Minister Oleg Serebrean, said last week that authorities were not insisting on the current practice of alternating the site of talks.

The country's criminal code, he said, sought to uphold Moldova's territorial integrity and was not aimed at Transdniestria's residents, though he could not offer security guarantees "because I am not a prosecutor".

Ignatiev holds Ukrainian and Russian citizenship, and Kyiv has ordered him appear in a Ukrainian court this month to answer charges of welcoming Russia's 2014 annexation of Crimea and for more recent hostile statements about Ukraine.

(Reporting by Alexander Tanas; Editing by Ron Popeskiand Leslie Adler)

By Alexander Tanas