Prosecutors told the court that the 377.2kg drug haul had a market value of Sh1.1 billion ($12.5 million).
Police also found 33,200 litres of liquid heroin whose value is yet to be established aboard stateless vessel.
Nine foreign nationals were charged in a Kenyan court on Thursday with trafficking the biggest ever single seizure of drugs at the port of Mombasa.
There has been a surge in the volume of heroin trafficked through east Africa in recent years, the United Nations Office on Drugs and Crime says, with Mombasa cited as a transit point for narcotics and other contraband.
The suspects, who included six Pakistanis, two Indians and an Iranian, denied trafficking the heroin and were detained until November when their trial will begin.
Prosecutors told the court that the 377.2kg drug haul had a market value of Sh1.1 billion ($12.5 million). Police also found 33,200 litres of liquid heroin whose value is yet to be established.
If convicted, the suspects face life imprisonment or a fine worth three times the value of the heroin, or both, a Mombasa-based lawyer told Reuters.
The drug is typically transported from Pakistan and Iran to east Africa, known for porous borders and weak maritime surveillance, and onwards to Europe.
The accused were arrested in Kenyan territorial waters in early July on board MV Bushehr Amin Darya, a stateless vessel, which was towed into the port of Mombasa, and police found the heroin hidden in the ship's diesel tank.
Kenyan police said they were communicating with India, Pakistan and Iran to find the owners of the vessel, which they said was headed for Mombasa at the time it was intercepted.
An Australian warship seized a dhow in Kenyan waters with more than a tonne of heroin worth $268 million in April. And in 2004, authorities seized 1.1 tonnes of cocaine from locations in in Malindi and Nairobi.
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