MEXICO CITY, Feb. 20 -- Three Salvadoran representatives to the Central American Parliament were kidnapped and killed during a trip to Guatemala for a parliamentary meeting, then their bodies were burned, authorities said Tuesday.

Among the victims was Eduardo Jose d'Aubuisson, the 32-year-old son of the late Roberto d'Aubuisson, founder of El Salvador's ruling Arena party. Representatives William Pichinte and Ramón González, as well as their chauffeur, were also killed in an assassination that investigators say they believe took place late Monday.

The presidents of El Salvador and Guatemala on Tuesday condemned the gruesome killings and announced plans to discuss the investigation Wednesday in Mexico, where they had previously been scheduled to attend a meeting with business leaders. The Central American Parliament posted a message on its Web site that called the killings "a massacre" and made an "energetic demand" that the two presidents conduct an immediate investigation.

"The authorities have not announced a theory about the reason for the killings, but observers of this criminal act have signaled that this was a planned killing carried out by professional assassins," Sigfrido Reyes, a member of El Salvador's legislature, said in a telephone interview Tuesday from El Salvador.

The victims were traveling Monday in a caravan with other members of El Salvador's delegation to the Central American Parliament, a regional body composed of representatives elected in the member states of El Salvador, Guatemala, Honduras, Panama, Nicaragua and the Dominican Republic, Reyes said. The caravan was escorted by Guatemalan police. For an unknown reason, Reyes said, the car carrying d'Aubuisson, Pichinte and Ramón González separated from the group in Guatemala City.

Their charred, unrecognizable bodies were found later that evening.

D'Aubuisson is the heir to one of El Salvador's most powerful political families. His father, who died of cancer in 1991, is one of the most influential figures in modern Salvadoran political history. The killing of the younger d'Aubuisson was being condemned Tuesday in El Salvador on the 16th anniversary of his father's death.

The U.N. Truth Commission found that the elder d'Aubuisson had ordered the assassination of Archbishop Oscar Romero, who was gunned down in March 1980 while presiding at a Mass during the Salvadoran civil war. The elder d'Aubuisson had also been linked by U.S. intelligence reports and former death squad members to an organization of paramilitary groups that killed thousands.

El Salvador's legislature Tuesday declared three days of mourning for Eduardo d'Aubuisson and the other victims of the kidnapping in Guatemala, Reyes said. Then, Reyes said, lawmakers waited for the bodies of their countrymen to come home.