* Panama government shows pictures of suspected missile parts
* Cuba confirms "obsolete" weapons were loaded at one of its ports
* North Korea under U.N. sanctions over nuclear weapons program
* Ship's captain attempted suicide (Updates with confirmation by Cuba that ship loaded there in paragraphs 4-6)
By Lomi Kriel
PANAMA CITY, July 16 (Reuters) - Panama seized a North Korean cargo ship it suspects was hiding missile equipment in a shipment of brown sugar from Cuba, after a standoff in which the ship's captain tried to slit his own throat.
The ship was stopped last week as it headed into the Panama Canal and authorities arrested the crew on Monday after finding undeclared missile-shaped objects - a potential violation of U.N. sanctions linked to North Korea's nuclear program.
"We found containers which presumably contain sophisticated missile equipment. That is not allowed. The Panama canal is a canal of peace, not war," Panama's President Ricardo Martinelli told local radio on Tuesday.
Cuba said on Tuesday evening that the ship was loaded at one of its ports with 10,000 tons of sugar and 240 tons of "obsolete defensive weaponry," according to a statement by the Cuban Foreign Ministry.
Cuba said the weapons were being sent back to North Korea for repair and included two anti-aircraft missile batteries, nine disassembled rockets, two MiG-21 fighter jets, and 15 MiG-21 engines, all Soviet-era military weaponry built in the middle of the last century.
In the statement, which was read out on the state TV evening news, Cuba said the weaponry was all required "to maintain our defensive capacity to preserve national sovereignty." It added, "Cuba maintains its commitment to peace including nuclear disarmament and international law."
Cuba has maintained warm relations with North Korea, including military and economic cooperation.
A high-level North Korean military delegation visited Cuba on July 1, according to official Cuban media reports.
A photo posted on Martinelli's Twitter page showed a long, green missile-shaped object with a tapering, conical end inside the ship, which he said was bound for North Korea.
A security expert said pictures showed radar systems for Vietnam-era, Soviet-made surface-to-air missiles.
The U.S. State Department praised Panama's decision to raid the ship, which it said had a history of involvement in drug smuggling, and warned the vessel would be violating United Nations Security Council resolutions by shipping arms.
The United Nations has imposed a raft of sanctions on North Korea, including strict regulations on arms shipments, for flouting measures aimed at curbing its nuclear weapons program.
Panama's security minister, Jose Raul Mulino, said his government had stopped the ship last Wednesday and had so far found two containers of military equipment.
He did not specify whether the cargo contained actual missiles but said the search could last up to a week.
When Panamanian officials began looking inside containers stuffed with over 250,000 100-kg (220-lb) bags of brown sugar, the captain became violent, Mulino said.
The captain, a North Korean citizen like the crew, tried to slit his throat with a knife, a police official said. The man was in hospital in stable condition, the official added, speaking on condition of anonymity.
Ben Rhode, a North Korea security expert at Harvard's Kennedy School of Government, suggested the captain's suicide attempt might have been an effort to escape severe punishment by officials in North Korea for failing to carry out his mission.
All 35 members of the crew of the ship, which is called Chong Chon Gang, were arrested after resisting Panamanian orders and are now being questioned at Fort Sherman, a former U.S. Army Base on the Atlantic end of the Panama Canal, the official added.
Mulino, the security minister, said that Panama would consult with the United Nations to determine which agency could charge the crew members for smuggling illegal weapons.
An official at North Korea's U.N. mission said nobody was available to comment on the ship.
A U.S. official said the most likely explanation for the cargo was that Cuba was sending missile system parts to North Korea for an upgrade, and sending sugar with them to pay for the work. A security official said Panama had asked U.S. experts to help inspect and identify the weapons.
The weapons seizure drew a stinging response from some U.S. critics of the island's Communist leadership.
U.S. Representative Ileana Ros-Lehtinen, the Florida Republican who heads the House subcommittee on the Middle East and North Africa, called on President Barack Obama's administration to cancel migration talks with Cuba this week.
North Korea is under wide-ranging sanctions enacted by the United Nations, the United States and the European Union, including a U.N. ban on all arms exports, due to its nuclear program.
"Shipments of arms or related materiel to and from (North) Korea would violate Security Council resolutions, three of them as a matter of fact," said U.S. Ambassador Rosemary DiCarlo, president of the U.N. Security Council this month.
"Obviously this shipment, if it's confirmed to have what we suspect, would be of interest to the (U.N. North Korea) sanctions committee," she told reporters in New York.
Previous violations of sanctions included North Korean shipments of arms-related material to Syria in November 2010 and rocket fuses for Iran in 2008.
The ship, built in 1977, was tracked leaving Port Vostochny, in Russia's far east, on April 12, according to Lloyd's List Intelligence, a maritime intelligence company. It was next registered arriving in Balboa, on the Panama Canal's Pacific side, on May 31, and crossed the waterway the next day heading for Havana.
It then disappeared from the tracking system and reappeared in Manzanillo, Panama, on July 11, according to shipping data obtained by research group IHS Maritime. IHS said there were indications it had changed cargo in the interim.
In 2010, the Chong Chon Gang was stopped by Ukrainian authorities who found small-arms ammunition and narcotics aboard the vessel, according to Hugh Griffiths, an arms trafficking expert at the Stockholm International Peace Research Institute.
A year earlier, the ship had stopped in Tartus, Syria, home to a Russian naval base, Griffiths added. (Additional reporting by David Alire Garcia, Gabriel Stargardter, Luc Cohen, Paul Eckert, Lucas Iberico-Lozada, Marc Frank and Louis Charbonneau; Writing by Dave Graham and David Adams; Editing by Doina Chiacu, Todd Benson, Peter Henderson, Claudia Parsons and Lisa Shumaker)