The US-Thailand talks, taking place in Great Falls, Montana, and lasting a week, will be the fourth round of wide-ranging discussions, a spokesman for the US Trade Representative's office said.

Most US farm groups support negotiations with Thailand, but the sugar lobby, having failed to secure an exemption from the US-Central American Free Trade Agreement, or CAFTA, reacted with alarm to the prospect of a trade deal with the world's second largest sugar exporter.

Sugar beet farmers met US and Thai officials on Monday to argue that sugar should not be included in the pact.

CAFTA, approved by the US Senate in a close vote last month, eliminates tariffs on US exports to Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and the Dominican Republic and expands the duty-free access those countries already have in the US market.