But Andrew Mwangura, head of the East African Seafarers' Assistance Programme, told Yonhap news agency in Seoul that the vessel was a South Korean cargo ship with 22 crew members on board and that it was taken Monday or early on Tuesday.
Choong declined to specify how many were on board but said that the figure of 22 was incorrect.
"The ship was hijacked by security men who were on board and were supposed to be protecting it. The reason for the hijacking is unclear," a port official said.
A spokesman for the African Union peacekeepers from Uganda, which guard Mogadishu's port, confirmed the seizure of the ship.
"It was far away from the seaport, it was at the anchorage. The hijacking was masterminded by the same people who were supposed to bring it into the docking," Captain Paddy Ankunda said.
Ankunda said the armed men were asking for $15,000 to free the freighter that arrived in the Somali capital 10 days ago.
The incident is the second piracy attack off the Somali coast in recent days.
On Sunday, a Japanese chemical tanker, with 23 crew members from Korea, Philippines and Myanmar on board, was hijacked off the coast of northern Somalia.
The fate of the ship and its crew remains unknown.