The president of neighboring Romania, Klaus Iohannis, warned in a letter to the European Council President Donald Tusk and European Commission President Jean-Claude Juncker that Moldova is "confronted with a very serious constitutional and political crisis" which could destabilize the country and the region.
Romania shares a common language and close historic and cultural ties with Moldova, where two rival political camps both claim to be in power, accusing each other of usurping the authority.
"I make an urgent appeal to you to identify, together with the European Union member states, concrete means to end the current situation the Republic of Moldova, through a negotiated solution, based on the values and principles of the European Union," wrote Iohannis.
Earlier on Wednesday, Moldova's police chief, Alexandru Panzari, fired six officers who publicly backed a new coalition government of Prime Minister Maia Sandu. Panzari is loyal to the previous leadership, which refuses to cede power.
Sandu's government was formed last weekend after months of political deadlock that followed an inconclusive election in February. But the former ruling Democratic Party, controlled by powerful oligarch Vladimir Plahotniuc, has refused to concede defeat. It has been backed by Moldova's Constitutional Court.
Sandu warned Panzari that he and anyone else obstructing the new government will face legal action.
"Every illegal action you take means heavy prison years for complicity or even participating in usurping state power," she said in a statement. She urged police officers and other public servants to ignore orders from the previous government.
Local media reported that Panzari prevented Sandu's interior minister, Andrei Nastase, from entering the police station where the six officers worked.
Sandu's coalition Cabinet comprises her pro-Europe ACUM party and the pro-Russian Socialist Party of President Igor Dodon. That government is backed both by Russia and the West, in an unusual show of unity.
However, Moldova's Constitutional Court - regarded as under the control of Plahotniuc - has said the government was formed after a 90-day post-election deadline and therefore is not valid.
On Sunday, the court dismissed Dodon as president, and appointed outgoing Prime Minister Pavel Filip as his replacement. Filip immediately called for parliament to be dissolved and snap elections to be held, a move Dodon called unlawful.
Dozens of supporters of the former government have been camping outside the state institutions since Sunday.
Sandu said the new government could call street protests as a display of public support. She expressed confidence that "millions" would come out, and called for calm and restraint.
Moldova, one of Europe's poorest nations, has been beset by political turmoil and rivalry between the West and Russia since it won independence after the 1991 collapse of the Soviet Union.
Vadim Ghirda in Romania and Jovana Gec in Serbia contributed to this report.
Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.