Panama has detained a North Korean-flagged ship coming from Cuba as it approached the Panama Canal with undeclared weapons, President Ricardo Martinelli said.
The weapons, hidden in containers of brown sugar, were detected after Panamanian authorities stopped the ship, suspecting it was carrying drugs.
The vessel was pulled over 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," Mr Martinelli told Panamanian television, without giving further details.
"You cannot go around shipping undeclared weapons of war through the Panama Canal."
Panamanian authorities have detained around 35 crew members.
Javier Caraballo, Panama's top anti-drugs prosecutor, told local television the ship was en route to North Korea.
Mr Martinelli claimed the captain of the vessel tried to take his own life after the ship was stopped.