Belgium has slammed the long jail term given to Thierry Falise

The three men were convicted of two charges - obstructing the work of police officials and possession of a weapon and an explosive device - in connection with the killing of a village security guard, sources at the trial said.

The trial, which according to Amnesty International inexplicably took place in a remote northern region and lasted little over two hours, has been described as a travesty of justice.

In Belgium, home to one of the jailed journalists, the Foreign Ministry summoned the Laotian ambassador to Brussels to "express to him our indignation and... dismay at the heaviness of the sentence inflicted on our countryman," Patrick Herman, a spokesman for the ministry said.

Diplomatic pressure

It is unclear whether the three - French cameraman Vincent Reynaud, Belgian photojournalist Thierry Falise and American pastor Naw Karl Mua - will be able to appeal against their sentence.

The men were reporting in an area off-limits to foreign media

"We are very concerned, although we continue to hope that a diplomatic solution remains possible. We hope that will be the case in the near future," Mr Herman added.

Paris-based press watchdog Reporters without Borders (RSF) went further, saying the trial was a farce and that Laos should be threatened with tough sanctions as a result.

"It is a country that lives off international aid - we must make it understand that it could pay dearly for behaving like a rogue nation," Robert Menard, the organisation's head said.

Swift justice?

The trial - which took place in Phonesavanh, 175 km (110 miles) north-east of Vientiane - lasted just two and a half hours.

Few independent observers were allowed to watch the court proceedings, and the accused men appear to have been given little opportunity to defend themselves, the BBC's correspondent Jonathan Head said.

According to numerous human rights reports... many of the Hmong in Laos have a poor standard of living, and often feel marginalised by the authorities The Hmong: Forgotten people of Laos

"Fifteen year prison terms after a trial lasting two hours defies belief" International human rights group Amnesty International said on hearing of the verdict.

"This show trial only confirms our continued concerns about fair trial and access to due process in Laos and makes a mockery of justice", it added in a statement.

Organisations campaigning for the rights of journalists believe the three were given heavy sentences because they were trying to cover the little-known conflict between ethnic Hmong rebel groups and the Laotian army.

The Laos Government denies the existence of the rebels, and bars journalists from operating in the country without official supervision.

Nothing is known about the fate of the four Lao nationals arrested with the foreigners. Our correspondent says that in the past, opponents of the country's strict communist regime have disappeared after being arrested.