The U.S. Embassy and a press freedom group criticized the trial, saying justice had not been served. France said it would work to obtain the return of the three men.
In a trial lasting about 2½ hours in the northern Laotian town of Phonesavanh, the three men were convicted of two charges — obstructing police work and illegal possession of a gun and an explosive device, said the sources who attended the trial.
French cameraman Vincent Reynaud, Belgian photojournalist Thierry Falise and the Rev. Naw Karl Mua, a Hmong-American pastor, were sentenced immediately after being convicted. They denied that they were involved in the killing of the guard.
Human rights groups have often said the justice system in Laos merely obeys its secretive communist rulers. According to the U.S. State Department's annual report on human rights, trial judges usually decide a defendant's guilt or innocence in advance.
The Laotian government is also accused of persecuting ethnic Hmong people, about whom Falise and Reynaud, both Bangkok-based freelance journalists, were trying to report with the help of Mua, their interpreter.
"I think it's appalling that the Laotian government would react with such stunning severity," said Lin Neumann of the New York-based Committee to Protect Journalists.
By handing down "that kind of a prison sentence, they send a message that Laos is unable to cope with external criticism or scrutiny," he said.
It was not clear if the three men can appeal, said the sources at the trial, contacted by telephone. They spoke on condition of anonymity.
The three were arrested on June 4, a day after what the government says was a nighttime clash between Hmong rebels and villagers that left one security guard dead in the village of Ban Khai. The government says the three men were part of the Hmong group.
The family sources said the court was told that a bag was found in a shack the morning after the clash containing a bomb and a gun. The seizure formed the basis of the charges.
Ban Khai is 30 miles from Phonesavanh, which is 110 miles northeast of the Laotian capital, Vientiane.
In a statement, the U.S. Embassy said it regrets the death of the village security official.
"Having said this, we do not believe that this trial and its outcome have served the cause of justice. The trial has fallen well short of international standards of jurisprudence," it said.
France said it would work closely with the United States and its European partners to obtain the three men's release.
"We hope that a diplomatic and humanitarian solution can be quickly found," said a statement from the Foreign Ministry.
Two Hmong rebels, who were arrested and tried along with the foreigners, were also convicted and sentenced to 15 years in jail, said the sources. A third rebel who escaped was sentenced in absentia to the same punishment.
The U.S. Embassy statement said all defendants were ordered to pay a fine of $1,000 each in addition to unspecified compensation to the family of the victim.
The statement said it is "deeply concerned" about the welfare of the five men. "We will continue to explore all avenues to see that Rev. Mua is able to return to his family in the U.S. as soon as possible," it said.
The three foreigners were escorted out of the courtroom at the end of the trial to a white Toyota van with its windows covered by curtains, which drove them away to an undisclosed location, said the family sources.
The Hmong rebels are the remnants of a CIA army that fought the communists during the Vietnam War before the communists came to power in 1975 by overthrowing the U.S.-backed ruling royal family. The Laotian government denies the long-running rebellion even exists and describes the guerrillas as bandits.
U.S. lawmakers in Minnesota, where the Hmong-American pastor lives as part of a large Hmong community, have said that efforts in Congress to normalize U.S. trade with Laos will falter over the case.
The most recent State Department report on human rights said that while a few people of Hmong descent were in the high ranks of the Laotian government, "societal discrimination against the Hmong continued."
However, "unlike in past years, there were no reports of government forces mistreating Hmong suspected of harboring insurgents," the report said.