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

Arriving at Bangkok airport, Belgian photojournalist Thierry Falise described his ordeal as "tiring", and said the two-hour trial in which he was convicted was "a mockery of justice".

Mr Falise - together with French cameraman Vincent Reynaud and Lao-American pastor Naw Karl Mua - were sentenced at the end of June on charges of obstructing the work of the police, and possessing a weapon and an explosive device.

Human rights activists criticised the heavy sentences, saying they were only given because the journalists were trying to cover the little-known conflict between Hmong rebels and the Laotian army.

Several ethnic Hmong were arrested with the foreigners, and are reportedly still in detention.

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

The release of the journalists and their translator comes after a flurry of intense diplomatic activity.

Last week, two days after the sentences were announced, ambassadors from France, Belgium and the United States held a hurriedly-arranged meeting with Lao officials to discuss the case.

Hmong: Forgotten people of Laos

They were told to arrange personal letters from their foreign ministers to the Lao foreign minister - letters which asked for the release of the three men on humanitarian grounds, and confirmed their respect for the laws of Laos.

Rumours circulated that a possible release could be linked to fears that aid to Laos would be cut if the men remained in prison.

But Lao Ambassador to France Pathammavong denied this, saying: "We are an independent country. We have received aid, but without conditions," he said.

The top-level letters may have provided a way of ending the incident whilst sparing the Lao Government any further embarrassment, says the BBC's Asia analyst Jill McGivering.

Torture claims

The human rights group Amnesty International welcomed the release of the three foreigners, but raised concern over the treatment of their Lao companions.

"They have reportedly already been badly tortured," Amnesty said in a statement.

Unlike the foreigners, the Hmong detainees are thought to have had no legal representation, and the precise charges against them are said to remain unclear.

"The international community must not ignore and wash their hands of the plight of the ethnic Hmong involved in the decades-old internal armed conflict that the journalists were reporting," Amnesty said.