The opposition say the results of the referendum were fraudulent

Minsk said the move was an unfriendly act reminiscent of the Cold War, and reserved the right to retaliate.

Sunday's referendum led to three nights of opposition protests in Belarus.

But election officials say nearly 80% of voters backed the poll, which allows President Alexander Lukashenko to stand for a third consecutive term.

The opposition says the result was achieved through fraud and intimidation.

The Organization for Security and Co-operation in Europe (OSCE) which sent dozens of observers, reported widespread problems with a simultaneous vote for parliamentary elections.

Pressure

US President George W Bush responded to concerns about the election and referendum with the Belarus Democracy Act which provides for sanctions against Belarus.

The act calls for the promotion of democracy by supplying aid to non-governmental organisations, helping to establish an independent media and a ban on US federal agencies from giving any financial aid to the country.

Belarus foreign ministry spokesman Andrey Savinykh said Belarus could take measures against the US in retaliation.

"The Republic of Belarus will continue to aim for mutually beneficial relations in international affairs, but we reject any attempts at diktat and pressure from the USA," he told Belarussian TV.

"In these circumstances, Belarus reserves the right to adopt retaliatory steps."