By Sabina Zawadzki and Dmitry Chubashenko

CHISINAU (Reuters) - Moldova's Communist president, Vladimir Voronin, accused neighboring Romania Wednesday of trying to overthrow his government and ordered mass arrests of protesters in Europe's poorest state.
Moldova's former Soviet master Russia backed Voronin's allegation of foreign interference but NATO and EU member Romania rejected the veteran leader's words as a "provocation."
Western powers urged all sides in Moldova to keep calm and avoid a repeat of Tuesday's riots, in which one person died, more than 270 people were injured and 193 were arrested.
Opposition parties called off further protests after the violence, when demonstrators contesting last weekend's Communist election victory set fire to the parliament building and broke into presidential offices.
Several hundred people remained outside the government headquarters demanding the release of those arrested during the riots.
After riot police retook the smoking and wrecked buildings overnight and rounded up the protesters, Voronin said he was expelling Romania's ambassador and introducing visa regulations for Romanians wanting to enter Moldova.
"When the flag of Romania was raised on state buildings, the attempts of the opposition to carry out a coup became clear," the 67-year-old Communist leader said. He vowed "strict punishment" for the ringleaders.
Most of Moldova, an ex-Soviet republic, was part of Romania until World War Two and retains close cultural ties with its larger neighbor. Moldovans are split between those wanting reunification with Romania and those keen to stay independent.
The Romanian Foreign Ministry said it was unacceptable that "the Communist power in Chisinau transfers responsibility for the Moldovan Republic's domestic problems on to Romania."
Voronin won strong backing from Russia which said the riots were aimed at undermining Moldova's sovereignty.
"We all saw under which flags these outrages have been carried out and hope that the European Union will draw the most serious conclusions about what happened," Foreign Minister Sergei Lavrov said in a statement.
Moldova is Europe's poorest country, with an average monthly wage of approximately $250.
In London, Fitch Ratings said Moldova's B minus credit rating could be threatened if political unrest in the mainly rural country persisted.
"There's already a fair bit of political risk built into Moldova's B minus rating but if the unrest is prolonged and severe and impacts the economy, we would expect to take some ratings action," said Edward Parker, head of Emerging Europe Sovereigns at Fitch Ratings.
RESIGNATION DEMAND
Opposition leaders condemned Tuesday's violence but demanded new elections. Some protesters demanded the resignation of Voronin, who is due to step down because of constitutional term limits but wants to retain power behind the scenes.
Vlad, a student demonstrating outside the government building, said the protest was an act of desperation.
"The election was a huge deception. We are protesting because there is no other solution. I am 20 now and have no future in this country," he told Reuters.
He denied that it was organized from outside: "It was the nation standing up, it was a revolution and it is continuing here. Young people were standing up by themselves. No one told them to do that."
Official results from Sunday's vote put the Communists ahead with close to 50 percent.
Vlad Filat, leader of Moldova's Liberal Democrats, accused the government of going back on an earlier pledge to hold a recount and forecast "some very serious repression."
The worst violence to hit Moldova's capital in decades could complicate efforts to resolve an 18-year-old separatist rebellion in the Russian-speaking region of Transdniestria, where Russia has had troops since Soviet times.
(Additional reporting by Peter Apps in London and Justyna Pawlak in Bucharest)
(Writing by Michael Stott and Guy Faulconbridge; editing by Andrew Dobbie)
Terra/Reuters