Malaysian police say they have arrested three Sri Lankans accused of trying to revive the Tamil Tiger rebel group.
They are accused of raising funds and spreading propaganda for the group.
A police spokesman was quoted as saying the suspects were senior operatives and had registered with the UN as refugees to "avoid suspicion".
The now defunct Tamil Tigers were crushed when their leader Velupillai Prabhakaran was killed by Sri Lankan forces in 2009 after years of war.
Authorities told the BBC's Sinhala Service that the three suspects had lived in Malaysia without valid visas for years.
"We found out that they have been trying to revive [the group] using their contacts in Europe and other countries," said one official, who did not wish to be identified.
Malaysia was now planning to deport them and was searching for more suspects, reported local media. There are currently 4,300 Sri Lankan citizens in Malaysia.
The arrest follows the killing in April of three men by the military in northern Sri Lanka.
The military said the men were trying to revive their organisation, which is officially known as the Liberation Tigers of Tamil Eelam (LTTE).
Although campaigners doubt there is an LTTE revival under way, the government maintains it is a real threat, correspondents say.
The group launched a violent uprising against the Sri Lankan government in 1983, seeking autonomy for Sri Lanka's Tamil-dominated north and east.
At their height of their power, the Tigers controlled nearly a third of of Sri Lanka's territory.
But they were defeated in May 2009 after Sri Lankan forces gained control of the last rebel-held area in the north-east, during which Prabhakaran was killed.
At least 100,000 people are estimated to have been killed in the 26-year civil war, and tens of thousands more were displaced.
There are still no confirmed figures for tens of thousands of civilian deaths in the last months of battle: estimates range from 9,000 - 75,000.
One UN investigation said it was possible up to 40,000 people had been killed in that time. The government puts the figure at 9,000.
The United Nations says it believes most of the civilian deaths in the final months of the war were caused by army shelling. The government denies the allegation.