* Ministry says blocked Facebook at junta's request
* Army says social media not blocked, blames gateway glitch
* Anti-coup protests organised on social media (Recasts, adds details)
BANGKOK, May 28 (Reuters) - Thai Facebook users were alarmed on Wednesday when the Information Communications Technology (ICT) Ministry blocked access to the site at the request of the military, but the junta blamed the brief shutdown on a technical problem.
Tweets, email and instant messenger traffic went into overdrive as confused users rushed to find out what had happened to Facebook, a site used by millions of Thais but inaccessible for about 30 minutes in the afternoon.
A senior ICT ministry official confirmed the site had been blocked to thwart the spread of online criticism of the military in the wake of a May 22 coup.
"We have blocked Facebook temporarily and tomorrow we will call a meeting with other social media, like Twitter and Instagram, to ask for cooperation from them," Surachai Srisaracam, permanent secretary of the Information and Communications Technology Ministry, told Reuters.
"Right now there's a campaign to ask for people to stage protests against the army so we need to ask for cooperation from social media to help us stop the spread of critical messages about the coup," he said.
Small protests have taken place daily against the regime, organised mainly on social media, testing the military as it seeks to assert its influence over the media and curtail dissent.
The junta has banned gatherings, imposed a curfew, arrested scores of activists and politicians and told print and broadcast media to refrain from critical reporting of the military. Foreign news channels like CNN, BBC and Al Jazeera have been blocked.
Small, brief protests have taken place in Bangkok as well as the northern and northeastern strongholds of the ousted government, erupting more like flash mobs than political rallies.
The military has also warned people not to spread what it considers provocative material on social media.
As Facebook went back online, a military official quickly appeared on television channels to reassure the public that the site had not been blocked and normal service would resume.
A spokeswoman blamed the outage on a gateway glitch.
"We have no policy to block Facebook and we have assigned the ICT ministry to set up a supervisory committee to follow social media and investigate and solve problems," said Sirichan Ngathong, spokeswoman for the military council.
"There's been some technical problems with the internet gateway," she said, adding that the authorities were working with internet service providers to fix the problem urgently.
The ICT ministry's hotlines were flooded with calls, and Twitter, WhatsApp and LINE were inundated with messages.
Posing for a "selfie" photo with his mobile phone, a policeman at a protest in downtown Bangkok said he doubted the government would go as far as shutting off social networking sites.
"Why would they block Facebook?," he said. "That would be madness."
But an office worker said there was too much vitriol on social media and blocking it would do no harm.
"If they've blocked Facebook then it's a good thing. There's too much information and hatred on social media," said Jay Jantavee, passing through Bangkok's bustling Victory Monument district. (Reporting by Manunphattr Dhanananphorn, Panarat Thepgumpanat and Amy Sawitta Lefevre; Writing by Martin Petty; Editing by Robert Birsel)