North Korea has accused Mexico of illegally holding one of its ships, after it ran aground last year.
It said the Mu Du Bong was a legitimate commercial ship and its detention a "rampant violation" of sovereignty.
But a UN expert says the ship belongs to North Korea's Ocean Maritime Management, which is on a UN blacklist.
In July 2013 one of its ships was seized in Panama after Soviet-era weapons and fighter jets were found hidden under sugar sacks.
United Nations sanctions ban most arms shipments to North Korea.
Under resolutions adopted after Pyongyang's nuclear tests in 2006 and 2009, the export of all arms and related parts, with the exception of small arms and light weapons, to the communist country is prohibited.
'Rampant violation'
The Mu Du Bong ran aground on a reef off Mexico's Veracruz state in July 2014. North Korea says it has since paid a bond to cover damage to the reef.