Japan's space agency has found particles that may be extra-terrestrial in the capsule of the space probe Hayabusa that returned home in June after a seven-year journey to an asteroid, reports said Wednesday.

Scientists discovered minute particles that may be from outside Earth, the Yomiuri newspaper and Kyodo News agency reported.

Their components have characteristics that differ from dust or aluminum powder samples that had been collected earlier and which had been believed to have originated from Earth, the Yomiuri said without naming its sources.

The Japan Aerospace Exploration Agency (JAXA) started a lengthy examination of Hayabusa's multi-layer sample canister on June 24 in cooperation with US space agency NASA.

It had confirmed that scientists found "minute particles" in the pod but it was unclear whether they were contaminants from Earth or from the Itokawa asteroid which Hayabusa landed on during its mission.

JAXA said it would hold a press briefing on progress in its analysis later Wednesday. It is expected to take months to get the final results.

Scientists hope asteroid samples could help reveal secrets about the origins of the solar system.

Hayabusa, which means "falcon" in Japanese, was launched in 2003.

Technical problems plagued the probe's journey. At one stage it spun out of control and lost contact with JAXA for seven weeks, delaying the mission for three years until the asteroid and Earth re-aligned.

When it finally latched onto the Itokawa asteroid, a pellet-firing system designed to stir up dust malfunctioned, leaving it unclear how much material the probe was able to gather.

After a seven-year space odyssey, the heatproof pod, fired back to Earth by the Hayabusa probe, landed in the Australian outback in mid-June.