Ex-Soviet Moldova on Tuesday urged citizens to stay calm and stepped up security after a series of blasts in a Russian-backed separatist region raised fears of a spillover from the war in Ukraine.
The breakaway region of Transnistria said there were explosions on Monday and Tuesday in the security ministry, a military unit and a radio tower belonging to Russia, and called them "terrorist attacks".
Transnistria is located about 80 kilometres (50 miles) from Moldova's capital Chisinau, bordering western Ukraine.
"We urge citizens to keep calm and feel safe," President Maia Sandu said after a meeting of the national security council.
She recommended stepped up patrols and vehicle checks near a buffer zone with Transnistria, tighter public safety measures and security checks on critical infrastructure.
The conflict in Ukraine has sparked fears in Moldova that it could become Russia's next target.
Ukraine accused Russia of staging the blasts with presidential aide Mykhailo Podolyak tweeting that Moscow "wants to destabilise the Transnistrian region and hints Moldova should wait for 'guests'".
The Kremlin expressed "concern" over the explosions. Russian state news agency RIA Novosti quoted a source in the Transnistria government as saying that attackers had entered from Ukraine.
The Organization for Security and Cooperation in Europe (OSCE), the world's largest security body, condemned "all attempts to destabilise (the) situation" in Transnistria and its buffer zone.
Two explosions hit a radio tower re-broadcasting Russian stations near the Ukrainian border early Tuesday, the interior ministry of the breakaway region said.
It also said offices of the state security ministry in the main city Tiraspol were hit by what appeared to be a grenade-launcher attack on Monday evening, a public holiday for Orthodox Easter.
Windows and doors were blown out and smoke was "billowing out of the buildings", a statement said.
Transnistria's security council said a military unit had been hit in the village of Parkany near the main city of Tiraspol.
- Russian speakers 'oppressed' -
"We are observing closely and the news prompts concern," Kremlin spokesman Dmitry Peskov said, while declining comment on who was behind the attacks.
Sandu said this was "an attempt to escalate tensions," and blamed "internal differences between various groups in Transnistria that have an interest in destabilising the situation".
Transnistrian leader Vadim Krasnoselsky suggested Ukraine was to blame and asked Kyiv to investigate the "illegal movement of... fighters on Transnistria's territory and their committing a terrorist act on our territory".
Transnistria declared a "red" level of terror threat for 15 days, stepped up security checks on roads and its frontier with Moldova, switched schools to remote learning and cancelled a parade commemorating World War II victory on May 9.
The unrecognised region seceded in 1990, followed by a short war in 1992, with Russian forces fighting alongside separatists against Moldovan forces.
In a frozen conflict, Russia has deployed troops there, guarding a stockpile of some 20,000 tonnes of munitions.
Chisinau has long called for the Russian troops to leave.
A senior Russian military official last week raised the issue of "oppression" of Russian speakers in Transnistria in the context of Russia's military campaign in Ukraine.
Moldova's foreign ministry summoned Russia's ambassador over the comments.
The former Soviet republic of 2.6 million people is one of Europe's poorest countries.
Unlike neighbouring Romania, it is not a member of NATO. It formally requested to join the bloc in March.