The military has clamped down on press freedoms since its coup last year, arresting reporters and photographers as well as revoking broadcasting licences while the country plunged into chaos.

Toru Kubota, 26, was detained near an anti-government rally in commercial hub Yangon in July along with two Myanmar citizens.

He was sentenced on Wednesday to seven years in jail for breaching a law that criminalises spreading information detrimental to state security and peace and tranquility, a junta spokesman said in a statement.

It added he had also received a three-year sentence for encouraging dissent against the military -- a charge that has been widely used in the crackdown.

The sentences would be served concurrently, the junta statement added.

A diplomat at Japan's embassy in Myanmar said Kubota also faces a charge of breaching immigration law, with the next hearing expected on October 12.

Japan's foreign ministry said it had been providing consular support and would "continue to appeal to the Myanmar authorities for the early release of Mr Kubota."

The filmmaker had arrived in Myanmar in July and was filming a "documentary featuring a Myanmar person", his friend Yoshitaka Nitta told a press conference in Tokyo in August.

According to a profile on the FilmFreeway website, Kubota has previously made documentaries on Myanmar's Muslim Rohingya minority and "refugees and ethnic issues in Myanmar".

- 'Slap in the face' -

Japan is a top donor to Myanmar and has long-standing relations with the country's military.

After the coup, Tokyo announced it would halt all new aid, though it stopped short of imposing individual sanctions on military and police commanders.

Kubota's jailing is a "slap in the face" for Tokyo, said Phil Robertson of Human Rights Watch.

"It's time for Japan to stop playing games, and move to support real international sanctions that will squeeze the junta's revenue sources."

In September, Japan's defence ministry said it would halt a training programme for members of Myanmar's military from next year over the junta's executions of four political prisoners.

The junta's execution of the four in July, in the face of international calls for clemency, was Myanmar's first use of capital punishment in decades and sparked international outrage.

Media watchdog Reporters Without Borders (RSF) said Kubota's arrest and "trial behind closed doors... is symptomatic of the military junta's abysmal disregard for the rule of law".

RSF's Asia-Pacific director Daniel Bastard urged Japan to stand-firm and obtain his release as "Myanmar's generals have become accustomed to using foreign journalists as bargaining chips in their relations with foreign governments".

Kubota is the fifth foreign journalist to be detained in Myanmar, after US citizens Nathan Maung and Danny Fenster, Robert Bociaga of Poland and Yuki Kitazumi of Japan -- all of whom were later freed and deported.

Fenster, who was held in May last year as he attempted to leave the country, faced a closed-door trial inside Insein on charges of unlawful association, incitement against the military and breaching visa rules.

He was sentenced to 11 years in prison before being pardoned and deported.

As of March this year, 48 journalists remain in custody across the country, according to the monitoring group Reporting ASEAN.

The military's crackdown on dissent since it ousted Aung San Suu Kyi's government has left more than 2,300 civilians dead, according to a local monitoring group.

The junta blames anti-coup fighters for the deaths of almost 3,900 civilians.