Police units Saturday prevented Contra rebel leaders from leaving two hotels where they came to negotiate their disarmament with the government. One Contra leader said they were being held ``hostage.'' Later in the day, members of a government investigative team announced they found no proof of Contra claims that the army massacred 14 rebels who had laid down their weapons. Contra leaders broke off the disarmament talks with the government on Friday demanding an investigation of the purported army massacre of the rebel fighters and 100 civilians May 18 near Waslala in Matagalpa province, 150 miles northeast of Managua. Contra commander Oscar Sovalbarro was named to the commission created Friday, but he remained in Managua on Saturday in a hotel where he said he and 18 other Contras were being held ``hostage'' by police. Sovalbarro said 10 other Contra leaders were prevented from leaving another Managua hotel. He said the rebels were considering a hunger strike in protest. The police who surrounded the Managua hotels did not appear to be threatening the rebels, but Contra leaders said they were told they could not leave the hotel grounds. Presidential spokesman Danilo Lacayo and Interior Minister Carlos Hurtado told The Associated Press that police had been placed at the hotel for the Contras' own protection. The leftist Sandinistas, who turned over power to President Violeta Barrios de Chamorro last month after losing February elections, still control the military and police. Sovalbarro, also known as Commander Ruben, said Saturday's police action showed the Contras ``have a good reason not to trust the government.'' He spoke from the garden of the Hotel Mercedes, where about two dozen police from the elite black beret unit were seen patrolling. The investigative commission, named by Mrs. Chamorro, traveled Saturday by helicopter to the area of the purported massacre and interviewed army and rebel leaders, said Santiago Murray, representative of the U.N. International Support and Verification Commission, at a news conference later in the day. ``We haven't been able to confirm the existence of any dead alleged by the Nicaraguan Resistance,'' he said. He said the commission members found no information about ``any dead or other serious incident.'' People interviewed near Waslala in the community of Zinica, where rebels alleged the incident occurred, seemed surprised by news of a massacre and said they had heard about it from a Managua radio station. The investigating commission consisted of government delegates, U.N. officials, Roman Catholic Cardinal Miguel Obando y Bravo and a Contra representative. A May 4 agreement between the Contras and the Chamorro government set a June 10 deadline for more than 11,000 rebels to surrender their weapons. But on May 19, the Contra high command suspended the disarmament, claiming authorities were not providing enough food, housing, jobs and security measures for fighters who lay down their arms. Only 1,404 of the rebel fighters have been demobilized, the government said. The U.S.-backed Contras fought the Sandinista government in a 10-year war that left 30,000 dead. The rebel fighters said they would give up their arms after Mrs. Chamorro, also backed by the United States, took over the presidency from Sandinista President Daniel Ortega on April 25. The Contras say their chief concern is that the army is controlled mostly by Sandinistas.