PERTH (AFP) - An oil slick sighted during the sea search for Malaysia Airlines flight MH370 did not come from the plane, officials said on Thursday, dashing hopes of finding a definitive answer to the fate of the jet.

"Preliminary analysis of the sample collected by ADV Ocean Shield has confirmed that it is not aircraft engine oil or hydraulic fluid," Australia's Joint Agency Coordination Centre (JACC), which is organising the search, said in a statement.

MH370 disappeared en route from Kuala Lumpur to Beijing on March 8 with 239 people aboard. Malaysian investigators believe it was deliberately diverted, though by whom is unknown.

Satellite data analysis indicated the plane crashed in the southern Indian Ocean, but no debris has been found despite a huge air and sea search. In the absence of wreckage, some relatives are publicly refusing to accept their loved ones are dead.

JACC said on Monday that the oil slick was sighted in the search area and would be taken to Perth for testing to see if it came from the Boeing 777.

Thursday's announcement was the latest setback in an operation marked by false leads and frustrated hopes.