Australian Navy sailors patrolling the coast of Africa have seized more than one tonne of heroin on a sailing boat.

The Navy estimates the street value of the heroin at $290 million.

Crew from HMAS Darwin boarded the wooden boat east of Kenya and discovered 46 sacks of heroin hidden among bags of cement.

The Navy says the drugs from the dhow were taken aboard HMAS Darwin.

The seizure was made as part of an international operation against drug smuggling in the Indian Ocean, the profits of which help to fund terror organisations including Al Qaeda.

The ship's commander, Terry Morrison, says the heroin seizure will put a dent in terrorist funding networks.

"These drugs have now been seized and are about to be destroyed," he said.

"It's well known that these drugs assist terrorist organisations through funding so that they can conduct violent acts.

"Today [HMAS] Darwin is proud to be able to remove these drugs from that funding stream."

The Navy ship is currently deployed on Operation Slipper.

It is part of the Australian Defence Force's contribution to the international campaign against terrorism, smuggling and piracy in the Middle East.

This area of operation encompasses an area of more than 2 million square miles, including the Indian Ocean.