Russia said on Sunday it had told Belarusian leader Alexander Lukashenko it was ready to offer military assistance if necessary as demonstrators gathered for one of the biggest protests against Lukashenko’s contested re-election yet.

At least two protesters have been killed and thousands have been detained since last Sunday’s vote, which opponents of Lukashenko, in power for 26 years, say was rigged to disguise the fact that he has lost public support.

He denies losing, citing official results that gave him just over 80 per cent of the vote.

The Kremlin said Russian President Vladimir Putin had told Lukashenko Russia was ready to assist Belarus in accordance with a collective military pact if necessary and that external pressure was being applied to the country.

It did not say where from.

There was tight security as Lukashenko’s supporters gathered in central Minsk for the first time since the election to voice their support for him and watch him give a fiery speech.

Lukashenko, under pressure from the European Union for cracking down on his opponents, said Nato tanks and planes had been deployed 15 minutes from the Belarusian border. Nato was not immediately available for comment.

“Nato troops are at our gates. Lithuania, Latvia, Poland and our native Ukraine are ordering us to hold new elections,” he said, adding that Belarus would “die as a state” if new polls were held.

“I have never betrayed you and will never do so,” he said.

Often emotional in state TV appearances, the 65-year-old leader had already alleged a foreign-backed plot to topple him.

Several thousand people attended the protest. Opposition media channels said Lukashenko, a one-time manager of a Soviet-era collective farm, had bussed people in from other parts of the country and that they were coerced into attending.

Reuters could not independently confirm that.

“The motherland is in danger!” an earlier speaker told the crowd, who chanted: “We are united, indivisible!”