BANGKOK – Thailand said it would hunt down "terrorists" it blames for the country's worst violence in 18 years in which 21 people were killed, but anti-government protesters say the army is to blame. A Thai "red shirt" protest leader threatened a mass march on army barracks where Prime Minister Abhisit Vejjajiva has been based, but that plan seemed up in the air as the country celebrates its new year. Deputy Prime Minister Suthep Thuagsuban ordered police to hunt for "terrorists" the government blames for the killings in Bangkok's old quarter which came after a month of generally festive protests and shocked the world. "We can't let terrorists walk freely in this country," he said. "We have enough evidence from still pictures and video footage that we can identify those carrying M-16 or AK-47 rifles where they live." The "red shirt" demonstrators, who want Abhisit to stand down immediately, said they would step up their protests, with plans to send out hundreds of motorcyclists handing out leaflets and pictures from the clashes in which 21 people were killed. Abhisit, who came to power in 2008 when the army brokered a deal in parliament, would have to step down if the Constitutional Court found his Democrat Party guilty of funding irregularities. The Election Commission on Monday unexpectedly recommended his party be dissolved for suspected funding irregularities. It is now in the court's hands. Surin Pitsuwan, secretary-general of the Association of South East Asian Nations, said the situation was deteriorating and must not be left to "fester." "The deteriorating situation in Thailand between demonstrators and government security forces in Bangkok has caused serious concern among ASEAN member states and the world at large," he said in an unusually bold statement for a group that tends not to criticize its members. "The situation is affecting the confidence in the security and stability in the region and if it is left to fester and escalate, it could lead to more violence and loss of life." U.S.-based rights group Human Rights Watch urged the Thai government to "keep its promise" to set up an independent commission to investigate the "violence and abuses by all sides."