Colombian authorities detained a vessel operated by China's largest shipping group for illegally transporting thousands of cannon shells, about 100 tons of gunpowder and other materials used to make explosives, the attorney general's office said.
The Da Dan Xia, operated by Cosco Shipping, was headed for Cuba when it was stopped on Saturday in the northern port of Cartagena, on the Caribbean coast, after the materials were detected during an inspection.
The cargo was listed in the records of the 28,451 deadweight-ton ship as grain products. The captain of the Hong Kong-flagged vessel had been arrested, the attorney general's office said.
China's Foreign Ministry spokeswoman Hua Chunying said the ship was carrying ordinary military supplies to Cuba and was not in violation of any international obligations.
"It is completely normal military trade cooperation. At present, China is communicating with Colombia on this matter," Hua said.
A Cosco Shipping official in the firm's Guangzhou head office said the ship was operated by the company but added she was unaware of the incident. Cosco Shipping is part of the state-backed China Ocean Shipping Group Co. (COSCO) conglomerate.
Cargo documentation the captain presented did not match the load the ship was found to be carrying, Luis Gonzalez, national director of the Colombian attorney general's office, told reporters.
"Around 100 tons of powder, 2.6 million detonators, 99 projectiles and around 3,000 cannon shells were found," Gonzalez added.
Photographs from the prosecutor's office showed wooden cases inside a shipping container with labels stating Chinese defense manufacturer China North Industries Group Corporation as the supplier.
The company, known as Norinco, is China's biggest arms maker.
A Norinco spokesman said by telephone that the ship was carrying some of its products, which had been sold legally, but that reported details of what was on board were "not true".
"Some media reports of what the ship was carrying do not accord with the reality of the situation," he said. "The products we sent over this time were mainly raw materials for the production of bullets. We have always been a responsible international company."
The recipient was stated as importer Tecnoimport in the Cuban capital Havana. The Cuban company could not immediately be reached for comment.
A man who identified himself as the Da Dan Xia's first officer confirmed the ship had been detained in Colombia when Reuters called the vessel's phone number on Wednesday. He declined to comment further.
China-Cuba ties growing
The attorney general's office said the ship's captain, Wu Hong, would be brought before a judge in order to be detained pending charges, and had been provided with an interpreter. Officials said he could be charged with illegal transport of military materials.
China is the fourth largest arms exporter in the world, according to the Stockholm International Peace Research Institute (SIPRI). Its three major customers are Pakistan, Bangladesh and Myanmar.
China and Cuba have increasingly close business ties, as well as political links because of their communist governments, but in Latin America, China is closest to oil-rich Venezuela.
President Xi Jinping visited Cuba last year at the end of a swing through the region, signing a series of deals, including debt restructuring and helping to build a shipping terminal.
A North Korean ship was detained in the Caribbean region in July 2013, near the Panama canal, when it was found to be carrying Soviet-era weapons from Cuba including two MiG-21 jet fighters, hidden under thousands of tonnes of sugar.
The United States and the United Nations both blacklisted two shipping companies which they said tried to hide the arms shipments destined for North Korea. Panama freed the ship and 32 crew to sail back to Cuba a year ago after most of a $1 million fine was paid.