Mr Sarksyan's Republican Party is widely expected to win the election

Results from two-thirds of polling stations showed Prime Minister Serzh Sarksyan's party was well ahead with 288,431 votes, election officials said.

Opposition groups said Saturday's vote was falsified and have called for mass demonstrations in the capital, Yerevan.

Armenian officials have insisted the election was calm, positive and lawful.

This is Armenia's fourth election since it gained independence in 1991.

Foreign monitors said the last poll, in 2003, did not meet democratic standards.

Ahead of the vote, Western countries warned of serious consequences if Armenia did not improve this record.

More than $200m of US development aid and the prospect of closer links with the European Union could be at risk if the polls are condemned as unfair.

'Grossly falsified'

Armenia's Central Electoral Commission announced o­n Sunday turnout had been almost 60%, higher than in the country's last election.

This has been o­ne of the worst elections possible Law-Governed Country Party spokesman

Preliminary results from 1,274 out of 1,923 polling stations showed Mr Sarksyan's Republican Party was in the lead.

The pro-government Prosperous Armenia Party was second with 129,683 votes, followed by the Armenian Revolutionary Federation, a former member of the ruling coalition, with 115,410.

Opposition groups were far behind, with the Law-Governed Country Party of former parliamentary speaker Artur Baghdasaryan winning 53,599 votes and the Heritage Party gaining 31,678.

A spokesman for the Law-Governed Country Party said the results reflected the widespread electoral fraud his party had witnessed.

"I fear these elections were grossly falsified," Tigran Mkrtchyan told the AFP news agency.

"This has been o­ne of the worst elections possible."

"Some pro-government parties were giving bribes of between 4,000 and 20,000 drams ($11-56) right in front of polling stations."

Mr Mkrtchyan said the opposition would organise mass demonstrations in Yerevan o­n Sunday to attempt to overturn the results.

Large protests after the country's last disputed election were broken up by police and the authorities have already warned they will not tolerate unrest.

The chairman of the electoral commission, Garegin Azaryan, denied the allegations of fraud.

"We can say that we had a positive election," Mr Azaryan said.

"The election was held in a calm atmosphere and in compliance with the law."

International observers, including the Organisation for Security and Co-operation in Europe, will issue a report o­n the election later o­n Sunday.