The United States introduced sanctions last week against four firms owned or controlled by a company linked to President Alexander Lukashenko in response to his government’s crackdown on political opponents.

“The introduction of fresh economic sanctions goes against the spirit of interaction and cooperation,” the Belarussian Foreign Ministry said in a statement.

“Thus, the Belarussian side has decided to freeze the project developed jointly with the United States on the exchange of highly enriched nuclear fuel.”

It said Belarus would “continue to maintain physical security of nuclear fuel in line with its international obligations on non-proliferation.” The deal will go ahead once sanctions are dropped, the ministry said.

Belarus, which has 220 kilograms of highly enriched uranium, according to US estimates, agreed in late 2010 to ship it to Russia with Washington’s help to be “blended down” into lower-enriched fuel.

Lukashenko tolerates little dissent and has maintained power since 1994 through election victories Washington considers illegitimate.

The new sanctions apply to the Belshina tire factory, the Grodno Azot fertilizer manufacturer, the Grodno Khimvolokno fiber manufacturer, and the Naftan oil refinery.

The four firms are owned or controlled by the Belneftekhim Concern, the largest petrochemical conglomerate in Belarus, which is already under sanctions for being owned or controlled by Lukashenko, the US Treasury Department has said.

The sanctions come at a time when Belarus is struggling to overcome a balance-of-payments crisis that has forced it to devalue its rouble and allow price hikes that have angered consumers and led to a wave of protests.