* Air, sea searches fail to find objects in southern Indian Ocean
* Australia studying satellite images to refine search
* No certainty objects from missing MH370 but best lead yet
By Jane Wardell and Siva Govindasamy
SYDNEY/KUALA LUMPUR, March 21 (Reuters) - Rescue authorities studied satellite data on Friday for more clues in the hunt for missing Malaysia Airlines Flight MH370, after an air and sea search in the remote Indian Ocean off Australia failed to find any trace of a suspected debris field.
Australia rushed four international aircraft to an area some 2,500 km (1,500 miles) southwest of Perth on Thursday when analysis of satellite images identified two large objects that may have come from the Boeing 777, which went missing from radar screens 13 days ago with 239 people aboard.
Investigators suspect the Malaysia Airlines flight, which took off from Kuala Lumpur for Beijing shortly after midnight on March 8, was deliberately diverted thousands of km (miles) and then crashed into some of the deepest, most isolated waters on the planet in a possible suicide.
Rescue authorities cautioned that the objects spotted on the satellite images, dated March 16, might not be related to the transcontinental search for the plane but said the find represented the best lead yet.
Four aircraft would resume the search of the 23,000 square km zone on Friday, the Australian Maritime Safety Authority (AMSA) said. A Norwegian merchant ship that had been diverted to the area on Thursday was still searching there. Another vessel would arrive later on Friday.
Acting Prime Minister Warren Truss said Australia continued to examine satellite footage to pinpoint the location of the suspected debris, which included a piece estimated from the satellite imagery to be 24 metres long.
"Clearly, there's a lot of resources being put into that particular area. It's broadly consistent with the flight plans that were talked about ever since the satellites and their work has been added to the information bank," Truss told ABC radio.
"That work will continue, trying to get more pictures, stronger resolution so that we can be more confident about where the items are, how far they have moved and therefore what efforts should be put into the search effort."
Strong winds, cloud and rain had made searching difficult, said Kevin Short, air vice marshal at New Zealand's Defence Forces which sent a P-3K2 Orion to search the area on Thursday.
"The crew never found any object of significance," he told Radio New Zealand. "Visibility wasn't very good, which makes it harder to search the surface of the water," he said.
A nearby desolate group of French-administered sub-Antarctic islands including St. Paul and Amsterdam and Kerguelen had been asked to look for debris, but none had been spotted, said Sebastien Mourot, chief of staff for the French prefect of La Reunion.
There have been many false leads and no confirmed wreckage found from Flight MH370 since it vanished off Malaysia's east coast, less than an hour after taking off.
There has also been criticism of the search operation and investigation, as more than two dozen countries scramble to overcome logistical and diplomatic hurdles to solve the mystery.
Investigators piecing together patchy data from military radar and satellites believe that, minutes after its identifying transponder was switched off as it crossed the Gulf of Thailand, the plane turned sharply west, re-crossing the Malay Peninsula and following an established route towards India.
What happened next is unclear, but faint electronic "pings" picked up by one commercial satellite suggest the aircraft flew on for at least six hours.
A source with direct knowledge of the situation said that information gleaned from the pings had been passed to investigators within a few days, but it took Malaysia more than a week to narrow the search area to two large arcs - one reaching south to near where the potential debris was spotted, and a second crossing to the north into China and central Asia.
Exhaustive background checks of the passengers and crew aboard have yielded barely anything that might hint at a motive for the flight's diversion out over the Indian Ocean.
But the staggered shutdown of the communications systems, and the plane's initial diversion west along navigational waypoints, have focused attention on the pilot and co-pilot.
The FBI is helping Malaysian authorities analyse data from a flight simulator at the pilot's home. Initial analysis showed that some simulator data logs had been deleted last month.
China's icebreaker for Antarctic research, Xuelong, or Snow Dragon, will set off from Perth to search the area, Chinese state news agency Xinhua cited maritime authorities as saying.
About two-thirds of the missing plane's passengers were Chinese nationals.
The satellite images, provided by U.S. company DigitalGlobe , were taken on March 16, meaning that the possible debris could by now have drifted far from the original site.
The relatively large size of the objects would suggest that if they do come from the missing aircraft, it was largely intact when it went into the water. (Additional reporting by Naomi Tajitus in Wellington, A. Ananthalakshmi, Anuradha Raghu and Niluksi Koswanage in Kuala Lumpur, Neil Darby in Perth, Byron Kaye in Sydney, Mark Hosenball in Washington, Nicholas Vinocur and Paul Sandle; Writing by Lincoln Feast; Editing by)
Our Standards: The Thomson Reuters Trust Principles.