Panama's president said on Monday that the captain of a ship from the Democratic People's Republic of Korea tried to kill himself after the vessel was stopped en route from Cuba and found to have suspected missile material on board.

A long, green missile-shaped object is seen inside the North Korean flagged ship "Chong Chon Gang" docked at the Manzanillo Container Terminal in Colon City July 16, 2013. Panama detained the North Korean-flagged ship from Cuba as it headed to the Panama Canal and said it was hiding weapons in brown sugar containers, sparking a standoff in which the ship's captain attempted to commit suicide. Panama's President Ricardo Martinelli said the undeclared weapons were detected inside the containers when Panamanian authorities stopped the ship, suspecting it was carrying drugs. [Photo/Agencies]

President Ricardo Martinelli said the ship was targeted by drug enforcement officials as it approached the Panama Canal and was taken into port, but a search revealed cargo of far greater concern.

The estimated 35-man crew also rioted when police boarded the ship, according to Martinelli, who said the suspicious goods were found hidden in a consignment of sugar.

The ship was intercepted near the port of Manzanillo on the Atlantic side of the canal.

"We're going to keep unloading the ship and figure out exactly what was inside," Martinelli told Panamanian television late on Monday.

Martinelli said the captain of the vessel tried to commit suicide after the ship was stopped. Panamanian authorities have detained the crew members. "The world needs to sit up and take note: You cannot go around shipping undeclared weapons of war through the Panama Canal," he said on Radio Panama.

"We had suspected this ship, which was coming from Cuba and headed to the DPRK, might have drugs aboard, so it was brought into port for search and inspection."

Initial reports said the ship was boarded on Friday.

"When we started to unload the shipment of sugar, we located containers that we believe to be sophisticated missile equipment, and that is not allowed," Martinelli said.

The ship, named Chong Chon Gang, is being held, as are the crew, who not only resisted the approach from the Panamanian authorities, but attempted to sabotage the search, he said.

The boat was headed back to the DPRK when it was stopped and taken to Manzanillo, east of the Atlantic opening of the Panama Canal.

The vessel "aroused suspicion by the violent reaction of the captain and the crew from Friday afternoon", Panama's Security Minister Jose Raul Mulino told the radio station.

And Javier Caraballo, an anti-drugs enforcement official, said: "Until now, we have not found drugs in the boat; we found military equipment."

Presidential spokesman Luis Eduardo Camacho said later that "at first glance" the cargo appeared to include missiles, but an examination of the ship by specialists may take as long as a week.

UN sanctions bar the transport of all weapons to or from the DPRK apart from small arms. Several of the country's ships have been searched in recent years.

AFP-Reuters