A group of jewelers in the United States is calling on Congress to change legislation so that gems mined in Burma cannot be imported to the U.S. from a third country.  Human rights advocates say that could help cut off funds to Burma's military rulers. But, industry experts say it would be very hard to enforce. Kate Woodsome reports from VOA's Asia News Center in Hong Kong.

The Jewelers of America sent a letter to U.S. congressional leaders this week asking them to close a legal loophole that allows Burmese gems into the country, despite sanctions against the military-ruled government.

The United States banned direct imports from Burma in 2003. But a year later, U.S. Customs and Border Protection issued a ruling allowing gems mined in Burma to be transported to the U.S. - as long as they are cut or polished in another country.

Basil Fernando of the Asian Human Rights Commission in Hong Kong says if the law is amended and enforced, it could slow the flow of money to Burma's military leaders.

"Money from the trade goes to the generals and their supporters, various companies, black marketers and various types of these groups. It doesn't go to the people in any way, even in a limited way," Fernando said. "Not even by way of any decent wage."

Jewelers of America is also calling on its 11,000 member retailers, including giants Cartier and Tiffany, to ensure gemstones are properly sourced.

It took the initiative after the Burmese military killed several people and arrested thousands who joined pro-democracy demonstrations in Rangoon and other Burmese cities last month.

Industry experts say it would be difficult to enforce an all-out ban on Burmese gems because it is hard to determine the stones' origin.

Stella Lee of the Gemological Institute of America in Hong Kong says a gem must be analyzed in a laboratory to know its origin. But she says even then, it can be hard to tell.

"Sometimes, if they do have, like, telltale inclusion or telltale properties, then we can tell is it (from) Burma. But then if they doesn't have any of these kinds of properties, we cannot really tell about the origin of rubies - the country of origin," Lee said.

Burma has a wealth of jadeite and sapphires, but it is world-renowned for its rubies. Lee says most high quality rubies sold on the international market are from Burma.

"The reason why people like Burmese rubies is they give you a more preferable color in the trade. Very, very deep, medium dark, pure red ruby," Lee said.

Industry experts say the majority of Burmese rubies come through neighboring Thailand, both legally and by smuggling. There, in a border town called Chanthaburi, companies heat-treat the rubies to improve their color and clarity. The gems are then cut and polished for sale to the U.S. and elsewhere.

Experts say, although rubies also are treated in India, Thailand's processing is unrivaled. It is the world's number one ruby exporter.

Industry insiders say a U.S. ban on Burmese gems likely would not stop the trade, because dealers are more interested in making money than in obeying the law.