At least one man killed and about 25 others were injured Tuesday when police and soldiers opened fire on a group of demonstrators who blocked a highway in northeastern Guatemala to protest a Central American free trade agreement with the United States, witnesses said.

President Oscar Berger (search) signed the accord into law Tuesday despite the protests. It must still be approved by the U.S. Congress.

Emergency workers in the city of Huehuetenango said a demonstrator identified as Juan Esteban Lopez, 32, had been killed in the Tuesday clash. The city's mayor, Mauro Guzman, said he believed the police had been fired on first.

"As far as I understand, they (police) returned fire after they were shot at by demonstrators," Guzman said.

Fabiola Hernandez, an office worker in the area reached by telephone, said she saw authorities shoot into a large group of farmers along a highway leading to the Mexican border, 170 miles (270 kilometers), northeast of the capital, Guatemala City.

While Hernandez refused to discuss injuries or fatalities, a witness named Marvin Rivas told Guatemala City's Radio Sonora that two people had been shot dead; however, police were unable to confirm either death.

The protesters were angry about last week's vote in Guatemala's legislature to ratify the Central American Free Trade Agreement (search).

On Tuesday, they also demanded the resignation of the interior minister and chief of police, and said they would continue the protests.

The United States signed the pact with Guatemala (search), El Salvador, Honduras, Nicaragua, Costa Rica and the Dominican Republic. Guatemala is the third Central American country to ratify the deal, which has not been ratified by the United States.

On Monday, demonstrators opposed to the agreement known as CAFTA, flooded the streets in Guatemala City and across the country.

Police used tear gas and a water cannon to break up a group of students in the capital after some pelted police guarding the presidential palace with rocks and bottles. Nineteen people were injured and 16 were detained in the uprisings.