The Ministry of Foreign Affairs (MFA) yesterday summoned ambassadors from the embassies whose diplomats showed up when Future Forward Party (FFP) leader Thanathorn Juangroongruangkit reported to Pathumwan police on a sedition charge on Saturday.
MFA spokesperson Busadee Santipitaks said ambassadors from the embassies were told to report to the ministry today, without elaborating.
Foreign Minister Don Pramudwinai earlier accused the foreign envoys of breaching diplomatic protocol and interfering in Thailand's justice system by being present.
"That could not happen in their own countries, but they did it in our country. We will ask them to cooperate and not do that again. It was against the diplomatic protocols of the United Nations," Mr Don said at Government House.
"As it has happened, there must be discussions on principles and etiquette to create understanding. It is basic conduct that embassies know about. The ministry has previously sent a letter and summoned ambassadors to tell them that such incidents are not appropriate."
Asked if foreign diplomats could have attended if they were invited, Mr Don said that in principle such an invitation was unacceptable because it concerned the justice system.
"Foreign embassies can assert their rights only when people of their respective countries are tried in Thai courts," Mr Don said.
"What happened is unusual. It's an intervention in our justice system," the foreign minister said.
"They think that they can do whatever they want in our country. We must ask Thai people whether it is appropriate for anyone to do anything when the feelings of Thai people are involved."
On Saturday, 12 diplomats from Australia, Belgium, Canada, Finland, France, Germany, the Netherlands, the UK and the US, as well as EU and UN human rights officials, went to the police station to observe the proceedings.
Mr Thanathorn was charged with sedition under Section 116 of the Criminal Code, helping a suspect escape under Section 189, and organising an assembly of more than 10 people that caused unrest (Section 215). If convicted, he could face respective jail terms of seven years, two years and six months for the three charges.
Police said the complaint dates back to 2015, when Mr Thanathorn, who was running his family's auto parts empire at the time, allegedly "provided assistance" to a leader of protesters against the 2014 coup who violated a junta ban on gatherings of more than five people.
Mr Thanathorn denied the charges and will give his written testimony on May 15.
His case will likely be handled by the Military Court, which deals with offences fitting the categories of the four offences allegedly committed between 2014 and 2015 when the National Council for Peace and Order (NCPO) seized power.
Prime Minister Prayut Chan-o-cha, also NCPO chief, yesterday said that he had instructed the MFA to explain to foreign diplomats that the issue involves the country's justice system.
The prime minister said authorities had followed the constitution and Thai laws.
"If we do not trust and adhere to our justice system, this will give others a chance to interfere," the prime minister said.
Deputy national police chief Pol Gen Srivara Ransibrahmanakul said that Mr Thanathorn's case, according to protocol, will be tried by a military court as the events happened at a time covered by an NCPO order stipulating such cases go to military courts.
Pheu Thai secretary-general Phumtham Wechayachai said yesterday that Thailand cannot afford to isolate itself from other countries and it was not surprising that foreign diplomats were interested in the issue.
"The international community wants to know why a civilian like Mr Thanathorn will have to be tried in a military court and the Foreign Ministry is duty-bout to provide an explanation," Mr Phumtham said.
Meanwhile, Future Forward Party secretary-general Piyabutr Saengkanokkul wrote on Facebook yesterday he has been summonsed to hear two more charges: computer crime and contempt of court involving a video clip of him reading the party's statement on the court's decision to dissolve the Thai Raksa Chart Party in early March.