Japan and India, meanwhile, added extra pressure on the United States by filing WTO compensation requests as a result of Washington's attempt to change the details of its obligations under the 1994 General Agreement on Trade in Services.

The filing by the two countries follows a similar request yesterday by the European Union, which said it wants the U.S. to open up other trade sectors to compensate for deleting part of the treaty.

The U.S., which said it was still trying to resolve the dispute with Antigua, explicitly removed online betting from the services agreement after losing a WTO ruling last year.

Antigua today said it is asking the trade body for authorization to target American trademarks and copyrights if the U.S. refuses to change its legislation.

WTO officials said they had received Antigua's request but were unable to provide details on its contents.

Antigua said the sanctions would come into effect "shortly," unless the United States requests a WTO arbitration panel on the level and scope of the sanctions.

"While we realize this is a significant step for Antigua and Barbuda to take, we feel we have no other choice in the matter," Antigua's Finance Minister L. Errol Cort said in a statement.

"Until such time as the United States is willing to work with us on achieving a reasonable solution to this trade dispute, we will continue to use every legitimate remedy available to protect the interests of our citizens," he said.

Gretchen Hamel, spokeswoman for the U.S. Trade Representative in Washington, said, "We will continue to work with Antigua and Barbuda to try to find a mutually satisfactory resolution to this dispute."

Antigua argues that before the ban was introduced, online gambling provided income for hundreds of its citizens and helped end its reliance on tourism, which was hurt by a series of hurricanes in the late 1990s.

Last year Washington stopped U.S. banks and credit card companies from processing payments to online gambling businesses outside the country.

The decision closed off the most lucrative region in a market worth $15.5 billion last year. About half of the world's online gamblers are based in the United States.