By Andrew Geoghegan, ABC News

The pirated ship is carrying Russian tanks and weaponry (US Navy: Jason Zalasky)

Evidence has emerged that a ship hijacked by pirates off the coast of Somalia is carrying weapons and tanks destined for South Sudan.

But the Kenyan government maintains that it ordered the military equipment.

Pirates holding a Ukrainian freighter and its crew off the Somali coast had been demanding $US20 million in ransom.

But they have reportedly halved their price.

However, the pirates’ demands are now being overshadowed by a controversy about the destination of the ship’s cargo.

The Kenyan government says 33 Russian tanks and other weaponry were destined for its army.

But a copy of the ship’s manifest indicates that Kenya may have ordered the equipment on behalf of the government of South Sudan.

If true it would be a huge embarrassment for Kenya, which helped broker an end to the civil war between South Sudan and the Sudanese Government.

South Sudan has denied it was involved.