A government official said yesterday that the lieutenant-general, who was declared Premier last month after the death of his predecessor Soe Win, will head to Singapore for the Asean annual summit.
Lao newspaper Vientiane Times also reported that Mr Thein Sein will pay an official visit to Laos today and tomorrow, at the invitation of Lao Premier Bouasone Bouphavanh.
The junta in Myanmar provoked world outrage in September when it violently cracked down on the biggest protest against its rule in 20 years, killing at least 10 people and locking up thousands of people. Diplomats put the death toll far higher.
Asean had in the past been reluctant to criticise its most troublesome member, citing its policy of non-interference in the internal affairs of member states. But the 10-member grouping has since condemned the crackdown.
Asean has also pledged to support the mission of UN special envoy Ibrahim Gambari, who is in Myanmar to try to convince the ruling generals to adopt democratic reforms.
Pro-democracy activists have been urging Asean to suspend the regime from the regional body, in the wake of the deadly crackdown.
AGENCE FRANCE-PRESSE, XINHUA