The choice of vehicle was almost inevitable. While describing his terrifying abduction ordeal in Sri Lanka, political activist Premakumar Gunaratnam said his captors came in a white van.

The Sri Lankan-born Australian citizen says he was grabbed by six to eight gunmen outside his house in Colombo in April, stripped and then 'sexually tortured' during his detention that lasted four days.

His colleague and fellow hard-left Marxist dissident Dimuthu Attygalle suffered a similar fate. He was also freed after four days in captivity, shortly after Gunaratnam was kicked out of the country.

Unlike others to have disappeared since the end of the country's Tamil separatist war in May 2009, they both lived to tell their tales after diplomatic pressure from Australia.

Being 'white-vanned' - it has become a verb synonymous with being abducted in Sri Lanka - was a widely reported tactic employed by the security forces to deal with troublesome opponents during the island's ethnic war.

But rights activists such as the Asian Human Rights Council say more than 50 people have been kidnapped in the past six months alone, highlighting what they say are continuing abuses on the Indian Ocean island that is re-emerging as a popular holiday destination.

"I believed they were going to kill me after they took me away at gun point," Gunaratnam, 47, told reporters via Skype from Australia after he was deported. "They blind-folded me, tied my wrists and legs and sexually tortured me."

"I am lucky to be alive and one of the very few to have survived an abduction by security forces. But, this is not a question about me, but about democracy and human rights in Sri Lanka," he added.

Attygalle, 43, a Sri Lankan national, said she was taken to the same place where Gunaratnam was being tortured.

"They said I should enjoy a comfortable life abroad without doing politics in Sri Lanka," Attygalle said. "I thought they would kill me, but I told them I expected something like this and that I am not afraid to die."

She was blindfolded and then later dumped in a Colombo suburb.

"Even after the official announcement of the end of that (Tamil separatist) conflict, there has been no end to abductions," the Hong Kong-based Asian Human Rights Commission (AHRC) said.

"A tacit policy that the use of abductions may be extended, not only to counter insurgency but also to the suppression of any opposition to the government, has been followed by all recent governments."

The AHRC said the only way Colombo could answer allegations of its involvement in the 'white van abductions' was by demonstrating 'credible action' to stop kidnappings.

The abductions of Gunaratnam and Attygalle came two weeks after the UN Human Rights Council (UNHRC) in Geneva urged Sri Lanka to probe alleged war crimes committed in the final stages of its war.

"Though the UNHRC called the regime to order... abductors in white vans have thumbed their noses at the world and continue to ply their trade with impunity," said Kumar David of the South Asia Analysis Group think-tank.

The government denies any involvement in the abductions and says police cannot be expected to prevent criminals using the tactic to settle scores.

Rights groups concede that at least some of the documented abductions are likely to be by criminals taking advantage of the climate of fear and the inability of police to find the perpetrators.

"You must understand that we are a country emerging from nearly four decades of war," spokesman and acting media minister Lakshman Yapa Abeywardena said.

"There may be several groups still carrying arms... Police can't be expected to be behind everyone to stop this."

In the cases of Gunaratnam and Attygalle, they were both luckier than Tamil newspaper editor N. Vidyatharan, 52, who was grabbed by gunmen as he attended a friend's funeral in Colombo suburb in February 2009, three months before the war ended.

Vidyatharan was bundled into a white van, stripped and assaulted. He was then handed over to the same police unit where Gunaratnam was dumped by his captors and held for two months without charge.

"Several big countries put a lot of pressure on the government when they heard I was abducted," Vidyatharan said. "I did not think they would free me. My prayer was for a quick death when they started assaulting me."

He has since given up his newspaper work and maintains a low profile.

Journalist Poddala Jayantha, 47, was mugged and taken away in a white van in June 2009, stripped and assaulted and then dumped on a roadside with a warning to stay away from media activism.

He said he had been a key figure organising the funeral of anti-establishment editor Lasantha Wickrematunga who was killed by unidentified gunmen in January 2009.

Police have so far made no arrests in connection with any of the high profile abductions and the Sunday Leader editor Wickrematunga's murder remains unsolved.