Three men were arrested today by counter-terrorist officers in London and Wales as part of a long-term investigation into the Tamil Tigers.
Scotland Yard said dawn raids took place at residential and business properties in Newtown, Powys, Mitcham, south-west London, and Surrey.
Two men, aged 39 and 46, were arrested at separate addresses in Newtown, and a third, aged 33, was held in Mitcham, a spokesman said.
All three men were arrested on suspicion of the commission, preparation or instigation of acts of terrorism.
They were to be questioned later today at high security Paddington Green police station in central London.
The spokesman said: "At 6.30am today officers from Counter Terrorism Command supported by Dyfed-Powys Police executed search warrants at a number of residential and business addresses in Newtown, Powys.
"Further warrants were executed at addresses in Mitcham and Surrey. Three men were arrested.
"A 46-year-old and 39-year-old were arrested at separate addresses in Powys and a 33-year-old was arrested in Mitcham on suspicion of the commission, preparation or instigation of acts of terrorism.
"This is part of a long-term investigation into alleged funding and procurement activity in support of terrorism overseas and two people have already been charged in connection with this investigation.
"It is not linked to al-Qa'ida-type activity or inspired terrorism. It is in relation to support, procurement and fundraising for a proscribed organisation, the Liberation Tigers of Tamil Eelam (Tamil Tigers)."
The LTTE is responsible for guerrilla attacks against armed forces and political targets in Sri Lanka, off the coast of southern India.
The rebels are fighting for autonomy for minority Tamils in the north and east of the island, claiming discrimination by the majority population.
More than 70,000 people have died in more than three decades of fighting and thousands have been forced to leave their homes.
The LTTE is thought to have power bases in both London and Paris, where sympathisers work to raise money for sophisticated weapons and other support.
More than 30 countries have proscribed the LTTE as a terrorist organisation, including the UK under the Terrorism Act 2000.
Two men, both from south London, have already appeared in court charged with terrorist offences in connection with the same operation.
One of the men is accused of arranging meetings of the Tamil Tigers and addressing an event in Hyde Park, central London.
He is also accused of amassing a hoard of military equipment including machetes, combat boots, camouflage clothes, spades and handcuffs. He denies the offences.
Last November, Tamil Tiger leader Colonel Karuna Amman was arrested in a joint operation by British police and immigration officials.
No details have been released of where he was detained or whether Sri Lanka will begin extradition proceedings.
Several days earlier, the head of the Tamil Tigers' political wing was killed in a wave of government air strikes in Sri Lanka.