LONDON - A joint operation by the British and Australian navies has seized the largest ever haul of heroin at sea, weighing 1,032 kilogrammes, the Ministry of Defence in London said Friday.The drugs, with an estimated British street value of more than £140 million (170 million euros, $235 million), were found on a dhow, or sailboat, some 30 miles (48 kilometres) off the coast of east Africa near Kenya and Tanzania. Commodore Jeremy Blunden, the British Royal Navy commander in charge of the operation, said the seizure was a ‘significant blow’ to drug trafficking networks.It was made as part of an international operation against drug smuggling in the Indian Ocean, which helps fund organisations such as Al-Qaeda. ‘This is the sixth seizure of heroin by the Combined Maritime Forces. since January and is by far the largest ever made by the organisation,’ said Blunden, who is based in Bahrain. He was commanding an Australian navy warship, HMAS Darwin, which has high-tech surveillance capabilities.‘Pinpointing a dhow in 2.4 million square miles of ocean is a real challenge,’ he added. An Australian navy team then boarded the dhow to find the drugs, which were stored in hundreds of plastic bags and hidden in a cargo of cement. They were later destroyed. The Combined Maritime Forces (CMF) is a naval partnership involving 30 nations covering 2.5 million square miles of international waters.