An Australian navy P-3 plane and a U.S. P-8 aircraft on Thursday failed to locate suspicious debris in search for the missing Malaysian flight, while a Norwegian freighter, the closest ship to the area, reportedly has arrived to join the search.

The Australian Maritime Safety Authority (AMSA) on Thursday posted on its Twitter account that the P-3 crew were unable to locate debris due to cloud and rain, which limited visibility.

It said further aircraft will continue the search for the missing Malaysia Airlines Flight MH370, which lost contact on March 8 en route from the Malaysian capital of Kuala Lumpur to Beijing.

The Australian government revealed earlier Thursday that they had spotted two objects possibly related to the missing plane in the southern Indian Ocean on satellite images, approximately 2,500 km southwest of the Australian port city of Perth.

However, the U.S. 7th Fleet's Commander William Marks said radar hits "of significant size" seen Thursday by a U.S. P-8 aircraft searching for the plane were not linked to the objects identified by Australian authorities.

The radar hits were "typical radar returns that air crew sees on a routine basis," Marks told Xinhua in an emailed statement. The U.S. P-8 aircraft has returned and landed in Perth, and confirmed that no objects were seen.

Norwegian freighter "The Hoegh St. Petersburg" from the Hoegh Autoliners was the closest ship to the area where the two objects were spotted by satellite four days ago. It reportedly has arrived in the area and started searching.

The Norwegian Shipowners' Association on Thursday said the freighter was asked to change its course to join the search. A spokesman for the association told Xinhua that any findings by the freighter will be reported directly to Australian search and rescue authorities.

It is a large area covering 100 square km and so it will take some time for the sailors to be able to spot something, said the spokesman.

The 230 meter-long freighter was on its way from Port Louis, Mauritius, to Perth when it was called to assist in the search.

Satellite and radar imagery confirmed by the AMSA as "credible lead" could be parts of the fuselage and wing of the missing Malaysian jetliner, a U.S. Navy source in Japan said Thursday.

Smaller objects detected around the two larger objects -- 25 meters and five meters long in size respectively -- could theoretically be debris from the plane, the Yokosuka Naval Base source said, requesting anonymity.

If the objects were confirmed to be parts of the missing MH370, the plane could possibly have made a soft-landing on the ocean rather than a nosedive as the debris has not been scattered, the source told Xinhua.

The source, an expert in maritime avionics, added that the satellite imagery was regarded as "highly credible."

U.S. company DigitalGlobe said Thursday that it has provided the Australian government with satellite imagery showing objects in the southern Indian Ocean that might be debris of the missing MH370.

"We can confirm that DigitalGlobe has provided imagery to search officials in Australia, and we have been informed by an Australian government official that it was our imagery ..." DigitalGlobe told Xinhua in an emailed statement.

Noting that it has no further information, DigitalGlobe pledged to "continue to cooperate with authorities to provide any and all information" to assist the search, said the U.S. provider of high-resolution satellite images.

Meanwhile, AMSA updated by midnight Thursday the information about the search operation related to the missing plane, saying the four aircraft it commissioned have covered an area of 23,000 square km.

"Four aircraft were tasked by the Australian Maritime Safety Authority on Thursday to a 23,000 square km area about 2,500 km southwest of Perth," AMSA said in its latest media release.

Another merchant ship is en route to the area. And the Royal Australian Navy ship HMAS Success is also en route to the search area. But it will take days for them to arrive.

AMSA said the search will continue on Friday.