The United States imposed sanctions Wednesday on two North Korean shipping companies over their attempt to ship arms from Cuba to North Korea in violation of US and UN sanctions.

Chongchongang Shipping Company and Ocean Maritime Management Company conspired to transfer a concealed shipment of arms and related materiel from Cuba to the Democratic People's Republic of Korea aboard a North Korean-flagged cargo vessel in July 2013, the Treasury Department said in announcing the sanctions.

State-owned Chongchongang Shipping owns and operates the cargo ship, Chong Chon Gang, which was found to be carrying undeclared containers of arms hidden under tons of sugar when it was stopped in the Panama Canal in July last year.

The arms shipment included components of surface-to-air missile systems and launchers, MiG-21 jet fighters parts and engines, shell casings, rocket-propelled projectiles, and other ammunition, the Treasury said.

The cargo was falsely declared to be sugar and spare plastic sacks and was hidden under 200,000 bags of sugar.

Ocean Maritime Management played a key role by providing its captain and crew with instructions to conceal the weapons and provide false documentation to the Panamanian authorities, the Treasury said.

"North Korea uses companies like Chongchongang Shipping and Ocean Maritime Management to engage in arms trading in violation of US and international sanctions," said David Cohen, the Treasury's under secretary for terrorism and financial intelligence.

"The Chong Chon Gang episode, in which the DPRK tried to hide an arms shipment under tons of sugar, is a perfect example of North Korea's deceptive activity, and precisely the sort of conduct that we are committed to disrupting."

The Treasury also blocked 18 ships in which the two companies have an interest, including the Chong Chon Gang.

The sanctions freeze any property of the designated entities that are within US jurisdiction, and bar their transactions with any US person or within the United States.