Testifying before a Senate Committee, Mr Powell said any softening of the sanctions against the island would only lead to the strengthening of the regime.

Mr Powell described as "foolhardy" attempts by other countries to engage Cuba. He did not specify which countries or investments he was referring to.

Last year the US Congress passed legislation allowing sales of food and medicine to Cuba - but the Bush administration has yet to introduce the regulations to implement them.

Mr Powell said he was not opposed to these measures which, he said, were an effort to promote "people-to-people" contacts between Americans and Cubans.

"We can have programmes that are directly with the people, contacts with people that don't go through the regime where he (Fidel Castro) can take his cut or use it to enhance his power," the secretary of state said.

'Anachronism'

Mr Powell said any other easing of sanctions which allowed inter-government or private-industry-to-government relations with President Castro's regime would be counter-productive.

He added that those who had tried to invest in communist Cuba had found themselves burned. Castro will "find a way to use those resources to enhance and strengthen the regime," he said.

Mr Powell did not name specific countries, but Washington has been critical of moves by Canada, Mexico and Venezuela to promote trade and business in the island.

The secretary of state said there was no chance of improved relations with Havana, until President Castro was out of power.

"It will happen, he will pass. He is an anachronism in the 21st century," Mr Powell said.

Washington imposed full economic sanctions against Cuba in 1962, three years after the revolution that brought Fidel Castro to power.

Critics say the main victims are Cuba's poor and sick.

Those who back an easing of sanctions argue that increased contacts between the US and Cuba would help to weaken President Castro's hold on power.