BANGKOK (Reuters) - Retired diplomat Maris Sangiampongsa has been endorsed as the country's new foreign minister by Thailand's king, the official Royal Gazette said on Wednesday.

Maris, 65, is a former Thai ambassador to Australia and Canada and was an adviser to predecessor Parnpree Bahiddha-Nukara, who unexpectedly resigned on Sunday after he lost his deputy prime minister position in a cabinet reshuffle.

The appointment comes at a crucial time as Thailand steps up diplomatic efforts in managing the ongoing conflict in neighbouring Myanmar, where a civil war between the ruling military and a loose alliance of established ethnic minority armies and a resistance movement is escalating.

Thailand in March started to deliver aid to Myanmar in a humanitarian initiative aim at paving the way for talks between warring camps.

Thailand has been pressing regional bloc ASEAN to be more proactive in trying to seek a solution following the failure of its peace plan to gain traction in the three years since it was announced. Several key members have become frustrated at the junta's refusal to engage their opponents.

"The direction is still there from the prime minister... (for Thailand) to be this kind of facilitator, mediator for the way forward in Myanmar," said political analyst Thitinan Pongsudhirak said.

"That objective is still there but the mechanics, they will have a lot to make up for," he said.

(Reporting by Chayut Setboonsarng, Panarat Thepgumpanat and Panu Wongchau-um, Edited by Jacqueline Wong and Michael Perry)