Opposition parties won enough votes to form a coalition
Moldova's governing Communist Party has lost its majority in parliament, according to preliminary results from Wednesday's election.
With 97% of ballots counted, the four main opposition parties have 50.7% compared with 45.1% for the Communists.
Opposition leaders say they will form an alliance if the result is confirmed.
Wednesday's vote was a re-run of the election in April, which was followed by days of violent demonstrations because of allegations of vote-rigging.
The Communist Party has been in government in Moldova, one of Europe's poorest countries, since 2001.
'Victory for truth'
If the preliminary results of Wednesday's election were confirmed, the Communists would have only 48 seats in the 101-seat parliament and its opponents 53 seats, the central election commission said.
Tom Esslemont, BBC correspondent, Chisinau
The Communists appear to have been blighted by their handling of the aftermath of the April elections and their attempts to discredit the opposition by blaming them for the violence. One analyst told me he felt that well educated Moldovans didn't buy the Communist propaganda, and became fed up with President Voronin's efforts to polarise society into two camps: "them" and "us ".
Another factor for their unexpected loss of public support could have been the defection, in May, of a charismatic Communist MP, Marian Lupu. He now leads one of the four "coalition" parties. But "coalition" is the pivotal word. Though the four parties say they will unite, they are not as similar in nature as they are in name.
They will find it difficult to elect a president as they do not have enough seats to do so without Communist help. But they do have enough to set up a government and to appoint several important posts including those of general prosecutor, chief of police and head of national security.
The opposition are likely to receive more votes when those won by three parties who failed to reach the 5% minimum threshold are redistributed.
The results are already being seen as a decisive success for the four pro-Western, pro-European parties, says the BBC's Tom Esslemont in Chisinau.
The leader of the Liberal Democratic Party, Vlad Filat, said the election was a victory for truth and that it would definitely seek to form a coalition with other opposition parties - the Liberal Party, the Democratic Party and Our Moldova Alliance.
"We will find the necessary compromise and find agreement so that Moldova finally gets democratic rule," he told the Reuters news agency.
Dorin Chirtoaca, the deputy leader of the Liberal Party, said the Communists would have to "join the ranks of the opposition and must not disturb Moldova on its path towards European integration".
"Democracy has won," he said.
Analysts say there is also the possibility that the Democratic Party, which won 12.5% of the vote or 13 seats, might forge a governing coalition with the Communists that would have a combined total of 61 seats.
However, the leader of the Democrats, Marian Lupu, a former parliamentary speaker who defected from the Communists, was dismissive of such a deal on Thursday morning.
"I know the mentality of the Communists. It is impossible to form a coalition with them," he said.
But despite the opposition's optimism there is a major obstacle to be tackled, our correspondent in Chisinau says.
The four parties have won enough seats to form a government, but not the 61 needed to meet the three-fifths majority required to elect a successor to the outgoing president and Communist Party leader, Vladimir Voronin, who has served a maximum of two terms in office.
Communist Party - 45.1%
Liberal Democratic Party - 16.4%
Liberal Party - 14.4%
Democratic Party - 12.5%
Our Moldova Alliance - 7.4%
Based on 97% of votes counted
Source: Central Election Commission
If the other parties cannot reach an accommodation with the Communists, parliament will be deadlocked.
The election was called because parliament was in stalemate over the same issue. April's vote gave the Communists 60 seats in the parliament, but not one of the opposition MPs backed their choice of president.
Now analysts say there is a need for dialogue between all parties.
However, it is too early to say how that co-operation might be achieved, our correspondent adds.
Mr Voronin, who was elected parliamentary speaker in May, said on Thursday only that the "most important achievement" of the vote was that Moldovans had been "able to organise civilised and democratic elections".
He later said in a statement that the Communist Party's share of the vote showed that "no other party can compare with it in terms of popular support".
"The Communist Party is ready for fundamental dialogue with all political forces represented in parliament," he added.
There has so far been no sign of unrest since the announcement of the results. Official turnout was 58.8%, up from 54% in April.
More than 3,000 foreign and Moldovan observers were supposed to be monitoring Wednesday's re-run, although one group pulled its 140 monitors out because some were barred, causing a storm of protest.