REPUBLIKA.CO.ID, BANGKOK -- A German rights group said Thursday that it has been ordered by Thailand's junta to cancel a briefing on the health of the kingdom's media landscape, in a growing clampdown on freedom of expression.

The ban came as two former ministers from the ousted government of ex-premier Yingluck Shinawatra were summoned by the military, which is escalating its campaign to crush dissent since seizing power last May.

The Friedrich Ebert Foundation said military officers had ordered them not to hold a briefing at a Bangkok hotel on Friday -- part of a series of annual reports looking at the challenges journalists face in different Asian nations.

"It's true, sadly. We were initially told over the phone and then the military went to the hotel and told them that we weren't allowed to hold the event," an employee of the foundation, who asked to remain anonymous, told AFP.

"We have released these reports every year for many years and have not had a problem until now," the employee added.

No junta officials were immediately available for comment.

Thailand's generals seized power in a May coup after months of disruptive, often violent street protests that led to the ousting of Yingluck's democratically-elected government.

An uneasy calm has since returned to the streets, but human rights groups warn that peace has been paid for with the severe curtailment of basic liberties.

Media freedom organisations say both self-censorship and enforced censorship has dramatically increased under martial law, with political gatherings and criticism of the military coup forbidden.

The country's strict lese majeste laws also mean domestic and foreign media outlets must heavily self-censor when reporting on royal issues.

The Friedrich Ebert Foundation -- which has ties to Germany's Social Democratic Party -- describes itself as an organisation promoting "the ideas and principles of social democracy".

Founded in 1925, it has had a presence in Thailand since 1970.

The halting of their briefing came as two former ministers who served under Yingluck were ordered to appear before the military, for yet to be explained reasons.

Chaturon Chaisang, a former education minister, told AFP he had been ordered to report to the First Army Region Headquarters at 3 pm (0800 GMT) but had not been told why.

Ex-foreign minister Surapong Tovichakchaikul was summoned earlier Thursday, junta spokesperson Colonel Winthai Suvaree confirmed. He has since been released.

"We will summon more people," he added.

After last year's coup, Thailand's generals ordered hundreds of people -- including academics, journalists, activists and ex-government ministers -- to report to them.

Many were detained for days and ordered not to speak out against the military.

Chaturon had refused and was eventually arrested in front of a large press pack at the Foreign Correspondents' Club of Thailand (FCCT) in Bangkok five days after the coup.

Earlier this week Surapong had met a top US diplomat who made critical comments of the junta during a visit.

Last September organisers of an event at the FCCT on post-coup human rights, including Amnesty International Thailand, were ordered to cancel it.

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