Satpal Singh Raghvir Singh, 41, was arrested in the suburb of Cheras for immigration offences on January 4 and deported to India yesterday.
"We believe he is part of a Sikh militant group called Babbar Khalsa International (BKI)," said Special Task Force (Operations and Counter Terrorism) Director Mohamad Fuzi Harun.
"He had been supplying the group with fake travel documents and using our country as a transit point for the group's activities," Harun said in a statement here.
Police apparently tracked down the suspected militant, who has been in the country since 2006, following the arrest of four BKI members.
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Another, named Daljeet Singh Tarsem Singh, was detained on May 13.
Satpal and the four, who have also been deported, are awaiting trial in India.
"We will continue to work closely with our counterparts in other countries to detect and eliminate such militant elements from within our borders," Harun added.