Panamanian authorities stopped the freighter on Monday when weaponry was found in amongst a load of 10,000 tonnes of sugar. The Panamanian president, Ricardo Martinelli, said the ship, identified as the 14,000-tonne Chong Chon Gang, had been carrying missiles and other arms "hidden in containers underneath the cargo of sugar".

Under current sanctions aimed at North Korea's nuclear weapons programme, all UN member states are prohibited from directly or indirectly supplying, selling or transferring all arms, missiles or missile systems and the equipment and technology to make them to North Korea, with the exception of small arms and light weapons.

The UN Security Council has imposed four rounds of increasingly tougher sanctions against North Korea since its first nuclear test on 9 October 2006.

The most recent resolution, approved in March after Pyongyang's latest nuclear test, authorises all countries to inspect cargo in or transiting through their territory that originated in North Korea, or is destined to North Korea if a state has credible information the cargo could violate Security Council resolutions.

"Panama obviously has an important responsibility to ensure that the Panama Canal is utilised for safe and legal commerce," said acting US ambassador Rosemary DiCarlo, who is the current Security Council president. "Shipments of arms or related material to or from Korea would violate security council resolutions – three of them as a matter of fact."

The 35 North Koreans on the boat were arrested after resisting police efforts to intercept the ship in Panamanian waters on Thursday as it moved toward the canal and take it to the Caribbean port of Manzanillo.

Panamanian officials were finally able to board the ship to begin searching it Monday, pulling out hundreds of sacks of sugar.

North Korea's government made no public comment on the case.

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