The actor was in Sydney for the Australian opening of Rocky Balboa Friday night, when he was stopped by customs officials after a routine X-ray detected something suspicious.
The actor and his entourage were detained for several hours, causing them to miss the film's premiere, for packing what was believed to be a type of human growth hormone.
Yesterday, officials searched his hotel room and private jet for illegal substances, just three days after seizing the banned substances at the airport.
Richard Janeczko, the national investigations manager for the Australian Customs Service, told Sydney's Daily Telegraph contraband items were seized, but refused to reveal any details.
Stallone, 60, initially told the newspaper the incident was a "misunderstanding" and that reports of him transporting steroids were "totally hot air."
When Australian officials arrived at the Park Hyatt hotel to issue the actor with a summons to answer charges on the prohibited substances, Stallone and his entourage were allegedly seen throwing things out the windows of their hotel room. According to the Telegraph, a search of the room allegedly resulted in additional evidence being seized.
The actor was cleared to leave the country on Monday, but an investigation will continue.
A spokesperson for the Customs Service adds, "There is a range of options we can pursue in these circumstances. The investigation is ongoing, and we are aware of Mr. Stallone's travel movements.
"The material has to be identified, and we have to look at all the options and the evidence before deciding what action to take."
Penalties for possession of such items in Australia can range from fines up to $110,000 or up to five years in jail.
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