YANGON, March 16 -- Myanmar's powerful army chief congratulated incoming president Htin Kyaw and pledged cooperation on Wednesday, after the ally of Aung San Suu Kyi was elected as the country's first head of state with no military background in decades.

Suu Kyi led her National League for Democracy (NLD) to a landslide election win in November, but a constitution drafted by the former junta bars her from the top office.

She has vowed to run the country anyway through a proxy president, and on Tuesday the NLD-dominated parliament elected Htin Kyaw for the role. He runs a charity founded by Suu Kyi and is a trusted member of her inner circle.

Relations between the armed forces and Suu Kyi will define the success of Myanmar's most significant break from military rule since the army seized power in 1962.

The armed forces hold a quarter of parliamentary seats and the constitutional right to nominate one of the three presidential candidates. The army candidate, retired general Myint Swe, was elected first vice president on Tuesday.

"It is hereby announced that the Tatmadaw takes pride in U Htin Kyaw's being elected as the President at the Second Union Parliament, and it will continue cooperating in every sector for the emergence of peace, unity and development," the Office of the Commander-in-Chief, Min Aung Hlaing, said in a Myanmar language post on Facebook.

Tatmadaw is the Myanmar language name for the military.

Min Aung Hlaing, who at the time of the historic vote was at a summit of Southeast Asian defence chiefs in Laos, issued the message several hours after the vote and long after outgoing President Thein Sein and representatives of other countries, including China and the United States, had extended their congratulations.

In the run up to the vote, the military questioned the qualifications of both Htin Kyaw and an NLD candidate for vice president, Henry Van Thio, underscoring tensions that have risen as the two sides started working on the details of the transfer of power.

Sources in Suu Kyi's camp say she has grown increasingly frustrated with military intransigence on issues ranging from amending the constitution to relatively minor formalities such as the location of the handover of power.

NLD lawmakers also say the military's choice of Myint Swe, who served the junta as head of the feared military intelligence and is on the U.S. sanctions list, goes against the spirit of reconciliation Suu Kyi is seeking to foster.