The United States said Monday it was reimposing sanctions on nine state-owned companies in Belarus after strongman Alexander Lukashenko ignored warnings to release political prisoners rounded up from democracy protests.

Since 2015, the United States has regularly issued waivers on sanctions for nine companies including oil firm Belneftekhim in recognition of small progress in Belarus, where Lukashenko has been in power for two and a half decades.

President Joe Biden's administration on May 31 warned it would go ahead with the sanctions unless Belarus releases prisoners and, on Monday, it gave the green light.

"This action is a further consequence of the Belarusian authorities' flagrant disregard for human rights and Belarus' failure to comply with its obligations under international human rights law," Secretary of State Antony Blinken said in a statement.

"The United States calls on the Belarusian authorities to immediately and unconditionally release all those unjustly detained or imprisoned," he said.

A woman wearing a carnival mask and holding an umbrella in the colors of the former white-red-white flag of Belarus marches in Minsk on April 6, 2021 to protest against what the opposition says were fraudulent elections
A woman wearing a carnival mask and holding an umbrella in the colors of the former white-red-white flag of Belarus marches in Minsk on April 6, 2021 to protest against what the opposition says were fraudulent elections AFP / STRINGER

The Treasury Department said that companies will have to wind up transactions with the Belarusian firms by June 3 or face US penalties.

Lukashenko, an ally of Russian President Vladimir Putin, claimed to win a sixth term in August elections that were widely criticized internationally and by the opposition as fraudulent.

State authorities responded to demonstrations with force and have sentenced hundreds of people to lengthy jail terms. Opposition leader Svetlana Tikhanovskaya, who says she won, fled to Lithuania.

Lukashenko on Saturday said that Russian authorities had derailed a plot to overthrow the government, a claim that the opposition denounced as a provocation that could be used to stifle dissent further.