Thai Prime Minister Thaksin Shinawatra left on Wednesday for neighbouring Myanmar, where he was due to have a rare meeting with the junta's reclusive leader, Senior General Than Shwe.
"It's for bilateral talks between two leaders on a variety of issues," Thaksin told reporters before leaving.
Thai officials provided few details on the hastily arranged trip but said the meeting would take place on Wednesday afternoon in Myanmar's new administrative capital, a place that few outsiders have seen.
Thaksin was due to return home later in the evening.
Most of Myanmar's government and military offices moved in February to a jungle compound, which Than Shwe has dubbed the "abode of the king," outside the central town of Pyinmana.
Thaksin made the trip with his army chief, General Sonthi Boonyarataglin, as well as Agriculture Minister Sudarat Keyuraphan, Foreign Minister Kantathi Supahmongkhon, and Environment Minister Yongyuth Tiyapairat.
The visit comes amid growing international pressure on Myanmar, formerly known as Burma.
US President George W Bush on Tuesday renewed economic sanctions on Myanmar over its failure to make democratic reforms and its human rights abuses, including the house arrest of pro-democracy leader Aung San Suu Kyi.
Last week Myanmar was the subject of heated debate at a meeting of the Association of Southeast Asian Nations, which also expressed concern over the regime's failure to move toward democracy.
While Thailand has also urged Myanmar to free Aung San Suu Kyi and make "tangible progress" toward reforms, Bangkok maintains close economic ties with the military-ruled state.
Thailand's largest energy firm PTT Plc said Monday it had joined the race against China and India in a bid for exclusive rights to Myanmar's northwestern natural gas reserves.
Thailand already pipes about one billion cubic feet of gas per day from Myanmar's offshore reserves in the southeast in the Andaman Sea.
Energy-hungry Thailand is also financing the construction of a series of dams on Myanmar's rivers near the border to generate electricity for its own needs.