AHMEDABAD - India's coast guard announced Sunday it had seized 1.5 tonnes of heroin worth almost $550 million from a merchant ship in what maritime authorities are calling their largest-ever drug bust. The ship was intercepted Saturday off the western state of Gujarat, the coast guard said in a statement. "This is the largest single haul of narcotics seized till date," it said, adding the drugs were worth an estimated $545 million. An undisclosed number of suspects were detained for questioning by coast guard officials, police and intelligence agencies.