Muhammad Shamin Mohamed Sidek, 29, and Muhammad Harith Jailani, 18, were detained in two separate cases in August this year, the Ministry of Home Affairs (MHA) said today.
Investigations showed that they had harboured the intention to make their way to Syria to join IS and engage in violence there, MHA said.
Shamin was influenced by IS' online radical propaganda and was earlier convicted and sentenced to three months' jail for inciting religious violence through his pro-IS postings on social media.
Subsequent investigations by the Internal Security Department showed that Shamin planned to travel to Syria to join IS once he had raised enough money to fund the trip.
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Shamin had also decided that if he was unable to join IS, he would consider fighting alongside a regional militant group that he considered to be aligned with the dreaded terrorist group which has occupied large swathes of land in Iraq and Syria.
The statement said 18-year-old Harith was also radicalised by online propaganda put up by IS.
He harboured the intention to carry out armed attacks for the terrorist group, MHA said.
"He was prepared to be trained by IS to fight and kill the group's enemies... Harith had collected information on how he could travel to Syria and also tried to radicalise those around him to support IS' cause in an attempt to recruit them to join IS together with him," the statement added.
"The Government takes a very serious view of any form of support for terrorism, including but not limited to the use of violence, and will take firm and decisive action against any person who engages in such activities," the statement added.