Moldova is Ukraine's "most fragile neighbour" and the consequences of Russia's nearby war are "too frightening to contemplate".
They were the words of UN Secretary General Antonio Guterres during a visit to Chisinau on Monday.
The UN chief's visit to Moldova -- not a member of NATO and one of Europe's poorest countries -- follows a series of unsettling incidents that have rocked Moldova's pro-Russia breakaway region of Transnistria.
Transnistria, a small strip of land with a population of about 470,000, has been under the control of separatist authorities since a 1992 war with Moldova.
Russia bases about 1,500 troops in the breakaway region, ostensibly as peacekeepers.
In late April, three men launched grenades at the region's state security office, and two large broadcast antennas were downed a day later.
On Friday, police in Transnistria said explosive devices were dropped from a drone leaving 1-metre-deep craters near a village.
"I am deeply concerned about the continuation and possible spread of the war Russia is waging in Ukraine," Guterres said, adding that Moldova's sovereignty and territorial integrity "must not be threatened or undermined".
"Moldova is on the frontline of preservation, peace and stability in the world. With war so close and with the divisions that are now. My hope is that there will be a clear sense of responsibility of all the actors."
Guterres held a joint press conference with Moldova's prime minister Natalia Gavrilita.
"Today, the Republic of Moldova is facing unprecedented crisis overlaps," she said. "But, regardless of the challenges, I assure you that the Republic of Moldova is on the path of development, democracy and European integration."