A government team, accompanied by a diplomat from Norway, flew to a rebel stronghold to discuss a key road linking the northern Tamil heartland with the rest of the island.
Rebel sources also say the two sides discussed ways to return conflict areas to normality and speed up the implementation of the ceasefire agreement.
Formal peace talks are due to take place in Thailand next month.
Tuesday's meeting between Bernard Goonatilike, the government's top peace negotiator, and SP Thamilselvan, the Tigers' political head, was the first time the sides had met face-to-face since 1995.
The BBC's Frances Harrison in Colombo says the talks, which took place in the northern town of Wanni, are another important step forward for the country's peace process.
Until now, both sides have been communicating through letters and intermediaries, including Norwegian officials who have been mediating in the peace process.
Suspicions
Tuesday's surprise meeting comes as the government and the rebels try to hammer out an agenda for talks expected at the end of June.
Mr Gunatilake said the two sides had discussed the issue of public transport and longer opening hours for checkpoints on the recently-reopened northern highway, which runs through rebel territory.
But he said the main aim of his trip was to avoid misconceptions on the part of the Tigers about delays from the government side.
The Tigers have been complaining that, under the terms of a February ceasefire accord, the armed forces should by now have vacated public buildings such as temples and schools.
Suspicions have been mounting on both sides in recent weeks - and our correspondent says this meeting should go a long way to dispelling them.
The Tigers have been fighting for an independent Tamil homeland in the north and east of the country since 1983.
The last round of peace talks broke down in 1995 after a 100-day ceasefire.
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