The trial of an American accused of preparing a revolt against the government of Fidel Castro was postponed Friday to give attorneys for both sides more time to prepare and so that an American attorney can observe the proceedings, government officials said.

Walter K. Van der Veer, 45, an electronics engineer from Miami, was to face a closed-door court in the case that could result in his execution. After the postponement, no new trial date was set.

Van der Veer’s arrest and Cuba’s call for his death have exacerbated tense relations between the governments of the United States and Cuba.

In Miami, attorney Ellis Rubin, who was hired by Van Der Veer’s wife, Nancy, said he hoped to travel to Havana on Monday. He said he did not know why the Cuban government decided to allow American lawyers to attend the trial. He said had been given no assurance he would be allowed to participate in Van der Veer’s defense.

“My task is to prevent Walter from being killed,” he said. “I think this places us in a position to negotiate with the Cuban government.”

In their first interview about the case, Van der Veer’s Cuban attorneys said they were grateful for the delay too. Their first formal meetings with Van der Veer were Wednesday and Thursday, and they said they want to be able to spend more time with their client.

Cuban authorities portray Van der Veer as a highly dangerous mercenary and said that he was trying to buy guns and explosives to attack government buildings.

U.S. State Department spokesman James Rubin in Washington said Friday, “We have serious concerns about legal proceedings and trials in Cuba and whether those proceedings meet international standards” of fairness.