Nairobi (AFP) - A record 1.5 tonnes of heroin have been seized off East Africa's coast since last month, according to United Nations figures, showing the growing importance of the route to international traffickers.
A total of 1,562 kilogrammes (3,444 pounds) of heroin were seized in a string of busts conducted by international warships patrolling the Indian Ocean in the six weeks since May 10.
The most recent seizure was at the weekend when Australian guided-missile frigate HMAS Newcastle seized 581 kilogrammes (1,280 pounds) of heroin aboard an unflagged dhow, with an estimated street value of $400 million (360 million euros).
The bust showed Australia to be "one of the world's most effective current heroin interdiction forces," said Brigadier Nagy Sorial, acting commander of the country's Middle East task force, in a statement.
In May and June, warships from Australia, Britain, France and New Zealand conducted joint operations in which 981 kilogrammes of heroin were discovered aboard six vessels, worth around $675 million (603 million euros).
Testing revealed the heroin to be "of a much higher purity" than usual, according to the Combined Maritime Forces (CMF) which conducted the busts.
- The 'Smack Track' -
"This is a great result, to bring together a coalition of ships and disrupt the trafficking of heroin in such an effective way," said Will Warrender, deputy commander of the 30-nation CMF which is deployed to patrol the Indian Ocean to stop piracy, smuggling and trafficking.
Because the heroin was seized in international waters no arrests were made, instead the drugs were dumped overboard and the crew and vessels released.
Alan Cole, head of the transnational organised crime programme at the UN Office on Drugs and Crime (UNODC) said "navies have responded to increased smuggling with an increase in the tempo of operations," leading to the high number of big seizures, he told AFP.
The previous biggest month for seizures was April 2014 when international navies seized a total of 1,221 kilogrammes (2,692 pounds) of heroin, including more than a tonne aboard a single dhow, again found by an Australian warship.
The southern route, nicknamed the Smack Track, leads from Afghanistan to the Makran Coast of Iran and Pakistan and across the Indian Ocean to East Africa, and is an alternative to the traditional opium trail via Central Asia and the Balkans.
The path was first revealed in 2010 when police busted four Tanzanians and two Iranians with 95 kilogrammes (209 pounds) of heroin in Tanga, northern Tanzania.
Since then seizures have grown exponentially. In 2014, nearly four tonnes of heroin were seized by international warships, almost double the amount found in 2013.
The head of Kenya's Anti Narcotics Unit, Hamisi Massa, says East Africa is "a key transit point" for heroin which is smuggled onwards to consumers in Europe and the US.