WASHINGTON, May 2 (UPI) -- The U.S. State Department said Thursday it had not yet decided what action, if any, it would take in response to the Belarusian expulsion of U.S. diplomats this week.

The expulsions are the latest step in an escalating confrontation between Washington and Minsk following the imposition last December of U.S. sanctions against a state-owned energy conglomerate. They came on the heels of a cyberattack on the Belarusian site of U.S.-supported broadcaster Radio Free Europe/Radio Liberty, which State Department officials blamed on the regime.

The expulsions reduced the size of the U.S. diplomatic staff in Minsk to four, department spokesman Tom Casey told reporters.

"We have told (Belarusian officials) that we have very serious concerns about this step that they have taken, and that means we need to think very carefully about our future and their future diplomatic presence in our respective countries," he said.

Casey denied earlier reports that the United States had decided to close its embassy in Minsk and order the Belarusian Embassy in Washington and its consulate in New York to close as well.