NSC secretary-general Paradorn Pattanabut said concern about the continuing rally by anti-government protesters at Uruphong intersection was the primary reason that ministers opted to extend the ISA.
Demonstrators have vowed to stay put amid police attempts to convince them to clear the area for traffic by moving to another rally site, preferably Lumpini Park, Pol Gen Adul Saengsingkaew told a cabinet meeting. Despite their defiance, the national police chief insisted he was confident officers could keep the protesters in check.
But Lt Gen Paradorn said he was concerned that demonstrators would try to shift protests to Government House if the ISA were revoked, claiming up to 65 anti-government factions could try and seize an opportunity to make their move against government.
The NSC chief did not elaborate on details of who the groups are, and stopped short of pointing to their connection with any political party. But he said the Network of Students and People for Reform of Thailand's protests at Uruphong would not be possible without outside support. Intelligence had indicated the protesters were receiving such support, but there is currently too little evidence to take legal action in the matter, he told reporters.
Lt Gen Paradorn said the forthcoming ruling on the disputed area near Preah Vihear temple could also be exploited to step up campaigns to bring down the government - both inside and outside of parliament.
The International Court of Justice has tentatively set Nov 11 as the date to decide whether its 1962 ruling includes the area in sovereignty disputes between Thailand and Cambodia.
The cabinet endorsement of the ISA extension came hours before the last order was due to expire at midnight on Friday.
Police have deployed 56 companies to handle the ISA, which has covered Dusit, Phra Nakhon and Pomprap Sattruphai since districts since Oct 9. Policing for the first nine days of the ISA was covered by a budget of 206 million baht.
Prime Minister Yingluck Shinawatra defended the extension, saying after the meeting that it was intended to prevent any incident that could lead to violence.
Democrat Party deputy spokeswoman Malika Boonmetrakul argued against the government's decision to extend the ISA, saying it was an unnecessary over-reaction to the Uruphong protests and curbed people's right to expression.