US Vice President Joe Biden thanked Panama Tuesday for detecting a controversial shipment of Cuban arms headed for North Korea apparently in violation of UN sanctions.

During his visit to tour an ongoing expansion of the Panama Canal, Biden said that the country "stepped up where others might have stepped back. ... You found and confiscated weapons heading from Cuba heading to North Korea.

"The United States is thankful for your taking that international responsibility, and you made a significant contribution, for real, to global security," Biden stressed.

Panamanian authorities seized the Chong Chon Gang July 10 after discovering 25 shipping containers of Cuban military hardware, including two MiG-21 fighters, concealed in a cargo of sugar.

Panama has said it believed that the shipment violated the UN arms embargo against North Korea.

In August, the Panamanian government said the United Nations had determined that the shipment violated sanctions against arms transfers to North Korea.

The sanctions were imposed over the reclusive country's controversial nuclear program.

Both Havana and Pyongyang said they were "obsolete" Cuban arms being shipped to North Korea for refurbishment under a legitimate contract.

The communist allies did not explain why the items were buried under more than 200,000 sacks of sugar inside the ship.

The ship's crew of 35 faces up to 12 years in prison if convicted on arms trafficking charges.

The sailors are being held at Fort Sherman, a former US military base.

Monday a North Korean delegation arrived in Panama hoping to be able to leave the country with most of the crew members.

The ship was fined a million dollars by the Panama Canal Authority for endangering the waterway. It has not yet been paid, Panamanian officials said.

Biden also met with President Ricardo Martinelli and toured the Panama Canal which is undergoing a massive expansion.

"To the 9,500 workers who are expanding this Canal, on behalf of the United States of America, thank you. Thank you for what you're doing," the US vice president said, enthused after his tour.

The $5.6-billion canal expansion, expected to be completed by 2015, will permit the passage of so-called "super-cargo" ships, which can carry up to 12,000 containers. Currently, the largest ships that can navigate the canal can carry up to 5,000 containers.

Allowing passage of these mega freighters will directly impact traffic at major US ports including Baltimore, Maryland; Charleston, South Carolina; and Savannah, Georgia.

As such, Biden brought along top US port officials, mayors and Transportation Secretary Anthony Foxx.

"Super-cargo" ships represent about 30 percent of the current world fleet, according to US sources.