Sri Lanka's military said on Tuesday it was trying to establish how the Tamil Tigers managed to buy light planes abroad, smuggle them onto the island and establish a rebel air force.
The probe follows the latest Liberation Tigers of Tamil Eelam (LTTE) air assault against the capital using two of their Czech-made aircraft.
The military shot down one aircraft just before it reached the intended target at the main airbase, while the second plane crashed into a tax building in Colombo on Friday night and exploded in a ball of fire.
"At this stage we do not know the exact origin of the planes except that they had been manufactured in the Czech Republic," Sri Lankan Air Force spokesman Janaka Nanayakkara said.
"Forensic tests are under way and we have asked the manufacturer about who owned these planes."
According to a local press report, the Zlin-143 planes may have come from a flying club in South Africa and been stripped down, smuggled in by sea and reassembled by the Tigers.
The Island newspaper also reported that rebel pilots may have been trained in South Africa, where the Tigers have a considerable support base among the expatriate Tamil community.
The military has said both planes involved in Friday night's attack were on a suicide mission, but intense ground fire had prevented a bigger disaster. Two people on the ground were killed and 58 wounded.
According to the island's defence ministry, the raid was the last air attack likely to be carried out by the Tamil Tigers -- who have lost nearly all of their northern fiefdom in a major government offensive.
"The security forces have put in the last nails on the LTTE's rudimentary air capability," the ministry said on Sunday, adding the Tigers deployed the aircraft because they would have lost them anyway to advancing ground troops.
Two weeks ago, the army said it had captured the last of seven air fields used by the Tigers. But the rebels may have used a patch of paved road in an area still under their control to take off, the ministry said.