
Veera Musigapong, Natthawut Saikua and Weng Tojirakan surrendered to police on April 14 following the dispersal of a large red-shirt mob at Government House.
"The extension of custody is necessary under emergency rule as a precaution against recurring disturbances if the three were to be granted bail," the court said in its ruling.
The red-shirt protest disbanded after riots erupted in parts of central Bangkok. Under emergency rule, police have a mandate to detain suspects for seven days instead of 48 hours before mandatory bail hearings are held.
In applying for temporary release, defence lawyers argued that the state of emergency had been wrongfully enforced.
However, the court struck down their argument on grounds that there was no judicial review disputing the government's mandate for emergency rule.
The three suspects appeared cheerful and were seen talking amicably among themselves and with defence lawyers during the bail hearing.
The next hearing is scheduled for next Wednesday, April 29. The three are being detained at the Border Patrol Police head-quarters in Pathum Thani.
The court is due to hold a separate hearing today in regard to the legality of the state of emergency.
The defence contends that Prime Minister Abhisit Vejjajiva imposed emergency rule on April 12 without seeking prior approval from the Cabinet.
Cabinet secretary-general Surachai Phuprasert and relevant officials are due to testify at today's judicial hearing on the steps taken to declare the state of emergency.
Meanwhile, a Pheu Thai MP claimed yesterday that fugitive ex-PM Thaksin Shinawatra had planned to return home on April 14, a day after soldiers cracked down on his red-clad supporters in Bangkok.
Lop Buri MP Suchart Lainam-ngern claimed Thaksin flew to a neighbouring country on a private jet on that day and was planning to enter Thailand via a northeastern province to solicit people before moving to Bangkok and join the red shirts.
He claimed Thaksin decided to return because that was the promise he had made if the Army started cracking down on his supporters. However, Thaksin's sister Yaowapa Wongsawat and MPs advised him against it, as they feared for his safety.