Belarus strongman Alexander Lukashenko said Saturday the country's sovereignty was under threat as police detained around 140 people during protests against his rule ahead of August 9 polls.

Lukashenko, who has dismissed the coronavirus epidemic as a hoax, is seeking a sixth term, having brooked no dissent during his nearly three decades in power.

Many of his critics have been jailed in recent weeks and on Saturday he said Belarus faced a major risk to its sovereignty and independence.

"I never thought there would be people in Belarus who would like to destroy the country," he said as he unveiled a monument in the country's east.

"No one will be allowed to betray or destroy what you and me have been building for a quarter of a century."

Opposition figures have fought hard to get on the ballot and enjoy robust support from the public, observers say.

Bucking expectations, a number of activists collected at least 100,000 signatures from supporters to be eligible to run.

Lukashenko's main rival Viktor Babaryko, a 56-year-old former banker, has collected 435,000 signatures, his aides say.

"People are tired of Lukashenko," said Vladimir Orlov, a 66-year-old writer.

In response to the simmering anger and criticism, Lukashenko has unleashed a crackdown on would-be election rivals and other opposition figures.

On Friday evening, people lined the streets in the capital Minsk and other cities for a second day of protests.

Valery Tsepkalo, a popular would-be opposition candidate, joined those rallies but police moved in to break them up.

As a result, around 140 people -- including 80 in Minsk -- were detained, the Vyasna rights group said. Detentions also took place in Vitebsk, Brest, Mogilev and other cities.

A number of journalists with foreign media outlets were detained. Some people were released late Friday.

The West has expressed concern over the latest detentions, with the UK embassy in Minsk saying "the detention of large numbers of journalists and peaceful protesters" was unacceptable.

Belarus riot police officers detain an opposition supporter at gathering Friday -- the second day of such protests -- for candidates seeking to challenge President Alexander Lukashenko in August polls
Belarus riot police officers detain an opposition supporter at gathering Friday -- the second day of such protests -- for candidates seeking to challenge President Alexander Lukashenko in August polls AFP / Sergei GAPON

Although relatively modest, such protests are unusual in Lukashenko's Belarus, analysts say.

"Society is polarised," independent analyst Valery Karbalevich told AFP.

"People's slogan today is: 'Anyone but him.'"

Lukashenko's main election rival Babaryko was arrested on Thursday on suspicion of financial crimes.

The next day Lukashenko announced his government had foiled a foreign plot to stage a popular uprising in Belarus.

Authorities claim Babaryko is in cahoots with "puppeteers" from Moscow.

Despite his arrest, Babaryko's aides on Saturday handed in his registration papers so that he is allowed to run.

"If Viktor Babaryko is registred a presidential candidate there is a possibility he might be freed," lawyer Maksim Znak said. "Or maybe not."

Babaryko formerly headed Belgazprombank, the Belarus subsidiary of Russian energy giant Gazprom.

Around 20 people have been detained in connection with the Belgazprombank case.

The general prosecutor's office opened a criminal case into organising or participating in a criminal group, with the penalty for those crimes up to 15 years.

The detention of Babaryko came after authorities jailed other critics including prominent opposition politician Mikola Statkevich, who is not allowed to contest the vote, and popular vlogger Sergei Tikhanovsky.

Tikhanovsky, 41, has particularly stood out, coining an insult for Lukashenko -- the "cockroach" --- and a catchy new slogan -- "Stop the cockroach."

Since then many Lukashenko critics have protested with slipppers in their hands.

Some said Lukashenko's refusal to introduce a coronavirus lockdown in Belarus, which has registered nearly 58,000 cases and more than 340 deaths, was an eye-opener.

"I have acquaintances who were his fans. They are now refusing to support him," said Valentina Svyatskaya, a 62-year-old pensioner.

"The authorities have done nothing to protect people and the coronavirus pandemic has become a catalyst."

The Organization for Security and Co-operation in Europe, an international election and war monitor, has not recognised any polls in Belarus as free and fair since 1995.