TOKYO - UN Secretary General Ban Ki-moon said Tuesday military-ruled Myanmar should release all political prisoners, including Aung San Suu Kyi, the country's jailed democracy leader.

He also called on North Korea to drop its nuclear ambitions after Pyongyang's second atomic test in May shocked the world, prompting the Security Council to step up sanctions in a new resolution.

"They (Yangon) should release all political prisoners, including Aung San Suu Kyi," said Ban, who was visiting Japan en route to Myanmar, where the Nobel Peace laureate has been detained for 13 of the past 19 years.

The Myanmar regime leaders "should immediately resume dialogue between the government and opposition leaders," he said after talks in Tokyo with Japan's Foreign Minister Hirofumi Nakasone.

The diplomatically risky visit starts Friday, the same day a Myanmar court is due to resume the trial of the 64-year-old on charges that she violated her house arrest after an American man swam to her lakeside home. She faces up to five years in jail if convicted.

While acknowledging worries over the timing of his visit, Ban said finding an appropriate time to visit Myanmar had been "a challenge" and said he wished to focus on relaying his message, which will includes calls on the junta to hold a democratic election.

"They should also create an atmosphere, a political as well as legal framework, conducive to the credible election which needs to... (be held) next year, in a most objective, transparent and democratic manner," he said. Aung San Suu Kyi, who leads the National League for Democracy, has been in detention or under house arrest for most of the time since the junta refused to recognise the party's landslide victory in Myanmar's last elections, in 1990.

Ban's trip to Asia also coincided with reports that a North Korean ship carrying weapons and related parts was headed to Myanmar.

Tensions in Asia have soared since North Korea's long-range rocket launch in early April and its second nuclear test in May.

In response to those actions, the UN Security Council approved a resolution which included a call on UN members to inspect North Korean cargo suspected of carrying banned weapons materials.

Pyongyang has however vowed to build more bombs and to start on a new weapons programme based on uranium enrichment.

Ban criticised the moves by North Korea, officially known as the Democratic People's Republic of Korea. "These measures taken by DPRK authorities run counter to the ongoing international community's efforts to realise nuclear disarmament and non proliferation," he said.

Nakasone said Japan stood ready to further cooperate with the United Nations to ensure implementation of the resolution.

Japan, which has taken a hard stance against North Korea, has historically maintained relatively friendly relations with Myanmar, the country formerly called Burma, and was previously its leading donor.

Tokyo drastically reduced development aid to Myanmar over human rights concerns, particularly after the junta cracked down on pro-democracy demonstrations led by Buddhist monks in 2007.

However, the Japanese government refused to join its Western allies in imposing sanctions on Myanmar.