The United States has imposed financial sanctions on Alexander Lukashenko, the president of Belarus, in response to what it called a fraudulent presidential election in March.
On Monday, President George Bush issued an executive order banning US companies from engaging in transactions with Lukashenko and other top Belarusian government officials.
Tony Snow, a White House spokesman, said: "These persons will not be able to access any assets that they might have in the United States, and US financial institutions, wherever located, will not be able to provide any financial services to them."
The move comes a month after the US imposed travel restrictions on Lukashenko.
The Belarusian president was re-elected in an election denounced by Western governments as rigged.
The order applied to Lukashenko and nine others including the internal affairs minister, the justice minister, the head of Belarus state televison and the president's national security adviser.
As a reason for the move, Snow cited the "fraudulent presidential election in March 2006, repression of post-election demonstrations, and continued detention of activists and opposition supporters, including former presidential candidate Alexander Kozulin".
Bush referred to Belarus in a speech on Monday to US Merchant Marines in Kings Point, New York, saying he wanted to see freedom extended to Belarus, "where we support the reformers seeking to erase the stain of dictatorship from Europe".
Last month, Lukashenko said his government would appeal to international courts, including the European Court of Human Rights, against travel bans imposed on him and other officials by the US and the European Union.
"What are the grounds for these restrictions? Is there some international court ruling that Belarusian officials are criminals,? No, this is crystal clear," he said.