Ships bound for Haitian ports may be stopped and searched by the six American, three Canadian and one French vessel on patrol around the island. There is no sign that the army is prepared to step down and restore the democratically elected president, Jean-Bertrand Aristide.
President Clinton, described as 'gravely concerned' with the crisis, yesterday signed orders freezing the assets of Haiti's leaders and their supporters, the White House said.
In Washington the Secretary of State, Warren Christopher, attacked a Republican attempt in Congress to limit Mr Clinton's ability to send forces to Haiti. The effort is unlikely to interfere with the blockade but will show the strength of opinion in Congress against any involvement that might lead to casualties.
Mr Christopher said Senator Bob Dole's amendment would be 'a very serious setback for the United States'. Anything limiting the ability of the President to use the armed forces was against the Constitution.
Republicans are getting some enjoyment from harassing Mr Clinton on this issue since in the past it was invariably Democrats who tried to restrict the use of armed force by Republican presidents.
Haiti is believed to have 10 weeks' oil supplies but when these are exhausted transport will be crippled.