Imran Kassim, 34, was issued a detention order in July for intending to undertake armed violence overseas, while Shakirah Begam Abdul Wahab, 23, was issued a restriction order in the same month for initiating and maintaining contact with foreign terrorist fighters.
The Ministry of Home Affairs (MHA) here said Imran, a managing director of a logistics company, was said to be radicalised by the Islamic State's (ISIS) propaganda.
He had also admitted that he was prepared to attack Singapore Armed Forces (SAF) personnel deployed in the global coalition to fight ISIS or hold them hostages to demand ransom from the Singapore government and use the money to boost the militant group's finances.
In February 2014, he travelled to Syria to oversee the delivery of humanitarian aid to a refugee camp that was arranged by the logistics company he worked for.
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He tried to slip away from his hosts at the refugee camp but was unsuccessful.
In July that year, he also took a pledge of allegiance to ISIS leader Abu Bakr al-Baghdadi, the Ministry said.
In March 2015, Imran had contacted a pro-IS foreign contact to facilitate his entry into Syria to join the militant group but did not receive any reply.
"His radical and pro-militant views attracted the attention of people close to him, who then reported him to the authorities," said the ministry.
It added that apart from wanting to join ISIS in Syria, Imran harboured intentions since May this year to join pro- ISIS groups that have laid siege to Marawi City in the southern Philippines.
The ministry said other suspect Shakirah had "actively initiated" online contact with ISIS foreign fighters operating in the conflict zone.
Shakirah, an administrative assistant, did so mainly because she enjoyed their attention, it added.
The ministry, however, also said that the duo, considered to be ISIS influenced, have been released from detention when their detention orders expired in August.