The department, calling Lo the "godfather of heroin", described him and his son as the "financial operatives" of Myanmar's generals with a history of illicit activities that supported their rule.

Asia World, it said, had been awarded numerous lucrative government projects, including the construction of ports, highways and government facilities, since it was founded in 1992.

Monday's announcement is the fourth time the US has imposed limited sanctions against Myanmar since the bloody crackdown on anti-government protesters in September last year.

'Deplorable situation'

George Bush, the US president, called for concerted international pressure on Myanmar to achieve a "genuine transition to democracy" and said the situation in the country "remains deplorable".

He said the military government was defying calls from its own people and the international community to begin a genuine dialogue with the opposition and ethnic minority groups.

"Arrests and secret trials of peaceful political activists continue," Bush said in a statement.

The sanctions entail the freezing of assets under US jurisdiction and barring Americans from conducting business with individuals and their families at the risk of heavy fines and prison sentences.

The US treasury also blacklisted 10 Singapore-based companies owned by Cecilia Ng, Law's wife, including property firm Golden Aaron.

Blacklisted 

Also included in the department's blacklist were the Aureum Palace Hotels and Resorts, and Myanmar Treasure Resorts, two hotel chains owned by Myanmar tycoon Tay Za, who was blacklisted in an earlier round of financial sanctions.

The sanctions drew criticism from Myanmar's South-East Asian neighbours, including Singapore, Laos and Cambodia.

But Adam Szubin, director of the treasury's Office of Foreign Assets Control, said some regional governments were quietly co-operating.

"It's incumbent on financial institutions and governments to take steps to keep dirty money out of their banks and their financial systems," he said.

"We see indeed financial institutions and governments taking those steps, sometimes not in the public view."