The decision was made in a special Cabinet meeting after the anti-government Network of Students and People for Thailand Reform vowed to indefinitely continue their demonstration at Urupong intersection on Rama VI Road.
Urupong is outside but adjacent to one of the three ISA-ruled districts which include Dusit, Phra Nakhon and Pom Prap Sattru Phai.
The security law activated on October 9 is due to expire today.
National Security Council (NSC) secretary general Paradorn Pattanatabut said the Cabinet prolonged the ISA use after learning that the rally would last longer than earlier expected.
In addition, there may be political activities after the International Court of Justice announces its judgement on the Preah Vihear temple dispute on November 11, he said.
He said the ISA is necessary to prevent protesters from intruding into the three districts but the government would focus on negotiations for their dispersal without taking harsh action.
Whether the ISA will be extended again after November 30 depends on the situation and the decision of the Centre for Administration of Peace and Order (CAPO), said Lt Gen Paradorn.
He admitted that the government was aware of possible negative consequences from using the ISA, but stability was the major concern.
“I can assure you that the demonstration would not have been as peaceful as it is if the ISA had not been in force,” he claimed.
“Police are not given full power under the existing laws in dealing with the demonstrators. Every civilised country needs a special law to maintain public order in a demonstration,” he said.
Prime Minister Yingluck Shinawatra said the Cabinet’s decision was in response to a proposal by security-related agencies and using the ISA could prevent violence and maintain public order.
She made no reply when asked if the use of the ISA could end before the new deadline of November 30.