A German rights group said Thursday the 29th January 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 Friday -- part of a series of annual reports looking at the challenges journalists face in Asia. "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. The employee added it was the first time they had faced such a problem. Thailand's generals took over after months of 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 rights groups warn that peace has been paid for with the severe curtailment of basic liberties. Media freedom organisations say that self-censorship and enforced censorship has dramatically increased under martial law, with political gatherings and criticism of the coup forbidden. Junta chief and premier Prayut Chan-O-Cha told reporters on Thursday that anyone who criticised his regime would be summoned. "Whoever comes out and criticises (the junta), they will be summoned," he said. "I am not autocratic. Why don't people understand and keep challenging me?" he said, appearing increasingly agitated under questioning. The halting of the briefing came as former education minister Chaturon Chaisang and ex-foreign minister Surapong Tovichakchaikul were ordered to appear before the military, for yet to be explained reasons. After last year's coup, the junta ordered hundreds of people -- including academics, journalists 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 in Bangkok. Earlier this week Surapong met with a top US diplomat who criticised Thailand's ruling regime during a visit. Junta spokesman Winthai Suvaree confirmed Surapong had been released after his summons, while Chaturon is still believed to be at army headquarters. A military source told AFP the junta will Friday summon Nattawut Saikuar, secretary-general of the opposition Red Shirt movement that supported Yingluck's government. Last September organisers of an event on post-coup rights, including Amnesty International Thailand, were ordered to cancel it.