COLOMBO, Sri Lanka — The politician knew something was amiss when a suspicious white van pulled alongside him at a Colombo park and four men got out, pretending to exercise. Ravindra Udayashanta alerted his supporters, and police. Soon, the gunbattle began.

In Sri Lanka, anyone who has crossed someone of importance is wary of white vans, said to be the vehicles of choice for shadowy squads who ‘‘disappear’’ opponents of powerful people. So, Udayashanta’s armed supporters immediately went into action.

‘‘I heard the crack of a gun and I too pulled out my pistol and fired back,’’ said Udayashanta, who had been involved in a long-running dispute with another ruling party lawmaker about a business deal. Udayashanta’s brother already had disappeared — dragged away one month earlier, he said, by men in a white van.

But things went differently on this March day. Udayashanta and his entourage surrounded the men from the white van and captured them. Eventually, at gunpoint, the men acknowledged who they were: Sri Lankan government soldiers.

In a country where people had hoped the 2009 end of its bloody, long-running civil war would mean a return to normalcy — a country with a history of disappearances that stretches back to the 1970s — the open secret of the white vans has come to exemplify the terror felt by anyone who runs afoul of Sri Lanka’s rulers

‘This is a sign of an uncivilized and undemocratic society,’

For years, little solid evidence had surfaced on the abductors.

Then came the cases of Udayashanta and that of another man in recent months— an Australia-based activist who says he was freed from abduction only under Australian pressure — who survived to tell their stories. In Udayashanta’s case, police confirmed that the men in the white van were government soldiers.

But neither case has done much to overturn Sri Lanka’s apparent culture of impunity. Police said the soldiers who got into a gunfight with Udayashanta were actually searching for deserters. Officials say the investigation is continuing, though it is unclear what — if anything — they are doing. Government leaders and the military deny any links to abductions.

Apathy on the part of many citizens over extralegal disappearances is partly to blame for their prevalence, said Ruki Fernando, an activist with the Sri Lanka human rights group Rights Now Collective for Democracy.

‘‘This is a sign of an uncivilized and undemocratic society,’’ Fernando said.

Rights activists, opposition lawmakers, and local journalists say top officials send abduction squads in white vans to kidnap political opponents, activists, and outright criminals. White vans are parked in front of the homes of government critics, in clear attempts to terrify them into silence. The citizen journalism Web site www.groundviews.com says that 58 people have disappeared during the past nine months. In at least 22 of those cases, witnesses saw the victims forced into white vans.

It’s not clear why white vans would be used, though many suspect it is because they are so common on Sri Lanka’s streets that they can quickly disappear into traffic.

A town council chairman in the Colombo suburb of Kolonnawa, Udayashanta said he had been on alert since his brother had been grabbed, an act he took as a warning from rivals.

Then, in March, a white van showed up again while Udayashanta watched a sports match in suburban Colombo. He pointed out the suspicious men to his supporters and police officers, prompting the men to scatter, triggering the gunfight and the eventual confession.

Udayashanta’s entourage said the men were the same ones who had abducted his brother.

The group later handed the suspects to police, who promptly released them.

Police spokesman Ajith Rohana confirmed the incident, and said the military confirmed the men were soldiers. He said Udayashanta was wrong to think he was being taken, that the men sought deserters.

Another man — Sri Lankan-born Australian citizen Premkumar Gunaratnam — was abducted in April but released a few days later after protests from Australian diplomats.

The former Marxist guerrilla, who was active in an armed rebellion in 1988-89 and now lives in Australia, had returned to Sri Lanka to start a new political party when he was snatched from a rented room.

‘‘All this happened within a few seconds . . . they stormed into the room and abducted me,’’ Gunaratnam said in an interview from Sydney. ‘‘They tortured me, interrogated, mostly humiliated me — some sexual torture as well.’’

His blindfold was removed long enough for captors to take a photograph, giving him an opportunity to see his surroundings, a well-maintained office with computers and stationery, Gunaratnam said.

His captors questioned him about the new party and whether he had links to the separatist Tamil Tiger rebels who were defeated in a civil war in 2009. Their manner suggested military backgrounds, he said.

Back in Australia, Gunaratnam’s wife Champa Somaratne and at least one lawmaker, Greens party Senator Lee Rhiannon, sounded the alarm about Gunaratnam’s disappearance. A few days later, the captors handed him to Australian officials at a Colombo police station, Gunaratnam said.

Australia’s foreign ministry would say only that it has urged Sri Lanka to ‘‘investigate fully all allegations of abductions.’’