South Korea's president won a promise from Myanmar to refrain from military cooperation with nuclear-armed North Korea during a two-day trip that included a meeting with opposition leader Aung San Suu Kyi.

Lee Myung-Bak's visit is the first by a South Korean leader to the country formerly known as Burma since a North Korean attempt to assassinate one of his predecessors in Yangon almost three decades ago.

Lee told reporters on Tuesday that he had urged President Thein Sein in talks a day earlier to refrain from any activities with North Korea that may "be considered as violating various UN Security Council resolutions".

Reports of military cooperation between Myanmar and North Korea have been a cause for concern for Seoul in the past.

Thein Sein denied any nuclear cooperation with Pyongyang, and said his country would abide by UN Security Council resolutions on the North's nuclear and missile programmes, a South Korean presidential spokeswoman told AFP. The resolutions also ban weapons exports by the North.

Myanmar has also agreed to free a North Korean refugee serving a five-year prison term since 2010 for illegally entering the country, the spokeswoman said.

The Myanmar leader, who has won international praise for a series of sweeping political and economic reforms since taking office last year, has previously denied any nuclear cooperation with the North.

In November a US official accompanying Secretary of State Hillary Clinton on a landmark visit said there were no signs "of a substantial effort" by Myanmar on acquiring nuclear arms.

Earlier Tuesday Lee visited the Martyrs' Mausoleum in Yangon where the then South Korean president Chun Doo-Hwan narrowly escaped an attempt on his life by Pyongyang agents in 1983.

Chun was saved from the bomb blast because he was delayed in traffic on his way to lay a wreath to commemorate Myanmar's independence hero Aung San, the father of Aung San Suu Kyi.

The explosion killed 17 South Koreans, including three cabinet ministers, and four Myanmar nationals.

Lee praised Suu Kyi's long struggle for democracy and said he was optimistic about the future.

"I believe that this country is now entering into a new era of change and I think that thanks to the leadership of Miss Suu Kyi that has become possible," he said, speaking through an interpreter.

The Nobel Peace Prize winner, who won her first seat in parliament in by-elections last month, said the pair agreed that "prosperity is no substitute for democratic rights" and sounded a note of caution about the reform process.

"We are at a point in the history of our country when there is a possibility for transition but I do not think we can take it for granted that this transition will come about," she said, following her meeting with Lee Tuesday.