"The investigation is continuing and the date of its completion is unknown," a customs official said. He refused to give details of the investigation, saying case materials were classified.
MiG-29 fighter plane - missing engines, ammunition, and "some other parts" - was discovered among containers and goods during a routine customs check on board a ship traveling from Ukraine to the United States on April 2.
The ship's owners had failed to include the aircraft in a special import license, and Hong Kong authorities impounded it pending completion of an investigation.
Ukraine's defense ministry earlier denied any connection with the aircraft.
Ukrspetsexport, Ukraine's sole weapons exporter, said it had sold the MiG-29 to a U.S. company as a museum exhibit or for scrap.
"This plane was sold in 2005 as a museum exhibit," a spokesperson said. "That is why it has been stripped of all weaponry and cannot be used as a combat aircraft."
The seizure is not the first time Soviet- and Russian-made military aircraft have been confiscated in Hong Kong, a special administrative region that enjoys a relatively large degree of autonomy.
In 2000, five Russian fighters being sent to the China Aviation Industry Supply and Marketing Corporation were confiscated over incorrect paperwork.
Under Hong Kong legislation, the maximum punishment for violation of customs regulations is a fine of 500,000 Hong Kong dollars (about $62,000) and a two-year prison term.
