Malaysia’s government is battling a growing threat from Islamic State — while critics of the ruling UMNO party are warning that extremism is being encouraged from within the country.

Prime Minister Najib Razak has urged his fellow ASEAN leaders, in opening a summit in Kuala Lumpur, that the organisation must present “a positive narrative of moderation, of hope and peace … because even in our ­region we are not spared the threat posed by extremism”.

Late on Monday, Malaysian police announced the arrest of 12 men linked to Islamic State, aged from 17 to 41, for plotting to attack government buildings in Kuala Lumpur. Explosives were seized when the men were stopped by police while heading for the mountains to allegedly test their bomb-making skills.

At the same time, Joseph Chinyong Liow, the inaugural holder of the Lee Kuan Yew chair in South-East Asia Studies at the Brookings Institution, analysing the extremism threat in Malaysia, wrote “while ‘external factors’ are important, the main causes for concern may well ­originate within Malaysia’s own borders”.

“The political and social ­climate that allows exclusivist right-wing groups and politicians to speak and act with impunity is the same one that will provide ­recruits and sympathy for insidious organisations such as ISIS,” Professor Liow wrote.