Roger Noriega, US assistant secretary for the Western Hemisphere, said on Friday there would be a "100 % inspection of flights to Cuba".
He added: "We're looking at agencies that do business that benefit the regime that we want to identify and cut off."
President George Bush announced the stricter measures in October as well as the creation of a Commission for Assistance to a Free Cuba.
The agency is headed by US Secretary of State Colin Powell and Secretary of Housing and Urban Development Mel Martinez "to shepherd a democratic transition in Cuba".
Noriega said: "Our efforts to enforce restrictions of financial transactions that benefit the regime has been stepped up in a dramatic fashion since the president's October 10 announcement."
The commission met for the first time on Friday at the White House with Bush's national security advisor Condoleezza Rice and others.
Anti-Castro Cuban exiles were
instrumental in electing Bush
The group is charged with drafting a report for delivery to Bush by 1 May on what each US government agency could contribute to accelerating and preparing for a transition in Cuba.
Noriega said the United States also wanted to make sure "that there will be no succession to the Castro regime but that there will be a profound and deep political and economic change that will benefit the Cuban people after a 45-year nightmare."
The United States has imposed punitive sanctions on Cuba for around 40 years, and Bush is the latest of 10 successive US presidents to openly seek to overthrow the Cuban government.
However, Cuba says US hostility does not stem from its government's human rights failings, but rather from its social and political successes and unyielding independence.
Cuba has achieved first world health and education standards, and its infant mortality and literacy rates now rival or outstrip those of the US, while its class sizes are a third smaller than in Britain.