A controversial referendum in Belarus has approved the lifting of a constitutional ban on a third term for President Alexander Lukashenko.
Belarus has become more isolated under Lukashenko
The EU and US have questioned whether Sunday's poll was free and fair.
Belarus' electoral commission head said preliminary results showed President Lukashenko had won 77.3% of the votes and the turnout was nearly 90%.
But an independent survey suggested Mr Lukashenko may not have gathered enough votes to change the constitution.
The poll, commissioned by the Baltic service of Gallup, said that if official turnout figures were taken into consideration less than the required 50% of the electorate could have voted yes.
Alongside the referendum, Belarus was also electing a new lower chamber of parliament - the House of Representatives.
Final results are expected later on Monday.
On Sunday, the BBC was shown what appeared to be evidence of irregularities in the voting.
A series of photographs from one polling station showed ballot papers which had already been marked with ticks beside Mr Lukashenko's name before they had been handed out to voters.
In one photo an elderly woman was given a marked ballot on arrival. Another image shows further ballots on a table with boxes already ticked.
The head of the Belarussian electoral commission said the allegations were false, but the Organisation for Security and Co-operation in Europe (OSCE), which is monitoring the elections, say they are investigating the claims.
Other reports said police had detained a number of people conducting an independent exit poll.
The website of the Belarus human rights group Charter 97 said the authorities had "rigged the referendum and the elections".
"Not a single democratic candidate has made it into parliament," it said.
It urged Belarussians to attend a protest rally in Minsk on Monday evening.
Earlier, the US State Department expressed "serious doubts" that the vote would meet international democratic standards.
Correspondents say the ex-Soviet republic has become ever more isolated under Mr Lukashenko, in power now for a decade.
Mr Lukashenko's rule has been characterised by the closure of opposition media outlets and the prosecution of opponents.
With the next presidential election due to fall in 2006, he claims that a third term is for the good of the nation, but his opponents have accused him of trying to become Belarus' leader for life.
The current constitution limits the president to two terms in office, but he has already once extended his rule by means of a referendum. In 1996 he prolonged his first five-year term by two years, to 2001.
He was then re-elected for another five years, in a poll which was criticised as undemocratic by Western observers.