MELBOURNE: Australian police launched a major murder investigation Friday after a three-year-old Indian boy's body was found dumped by a Melbourne roadside, threatening to cast a fresh shadow over ties.

Victoria state premier John Brumby said he found the killing of Gurshan Singh, who was visiting from Punjab in northern India, "personally distressing" but urged people not to make any presumptions about motive.

"What has occurred is an unthinkable tragedy. It's deeply, deeply distressing," Brumby told reporters.

"There are no visible signs of the cause of death at this stage... but I think it's very important that no one jumps to conclusions," he added.

Singh disappeared from a suburban house at about 1:00 pm (0200 GMT) Thursday while his mother was taking a shower. His body was found about six hours later some 30 kilometres (20 miles) away, not far from the city's airport.

His death comes as Foreign Minister Stephen Smith seeks to smooth over relations with India, a major export market, after a series of alleged race attacks including the killing of an Indian student in Melbourne in January.

Smith, the latest in a series of top officials to visit India in recent months, met Prime Minister Manmohan Singh on Thursday and assured him "that the Australian government was taking the issue of Indian student safety seriously. "Prime Minister Singh said he appreciated the Australian government?s efforts to address this issue," the foreign minister said in a statement.

Brumby said state police were using "every possible resource" and their "best investigators" to track down whoever killed Singh, and appealed for witnesses.

Police experts are carrying out further forensic tests after an autopsy failed to reveal the cause of death.