Japan's Asahi Shimbun newspaper reported North Korea tried to ship materials suitable for uranium enrichment or missile development to Myanmar via China. It said Japanese authorities seized metal pipes and high-specification aluminum alloy at U.S. request when the ship docked in Tokyo in August.
Sen. Richard Lugar, a leading voice in Congress on nonproliferation, wrote Tuesday to Myanmar's President Thein Sein, urging him to disclose the intended recipient of the materials and their planned use. The Associated Press obtained a copy of the letter Thursday.
The reported seizure heightens concern over whether Myanmar is making good on promises to sever military ties with North Korea, believed to have assisted Myanmar in ballistic missile technology. Myanmar denies having sought nuclear assistance.
Lugar commended reformist leader Thein Sein for recently agreeing to sign up an international agreement that would allow greater U.N. scrutiny of any nuclear activities.
He said the reported Japanese seizure also provided an opportunity for the Myanmar government to demonstrate transparency.
"Peace and stability within ASEAN are potentially impacted by the intended purpose of the ship's cargo," Lugar wrote. ASEAN is Southeast Asia's regional bloc and Myanmar is a member.
Thein Sein has ushered in democratic reforms after decades of direct military rule, helping end the nation's international isolation. Earlier this month, Barack Obama became the first U.S. president to visit the country, also known as Burma.