Image copyright Reuters Image caption The possible signal was detected by an Australia P-3 Orion searching the southern Indian Ocean

A plane searching for missing Malaysia Airlines flight MH370 has detected a possible new signal in the southern Indian Ocean, Australian officials say.

An Australian P-3 Orion aircraft picked up the signal in the same area where an Australian vessel detected audio pings earlier this week, officials said.

The signal would require further analysis, but could have been from a "man-made source", officials said.

Flight MH370 vanished on 8 March, with 239 people on board.

The search zone was tightened on Thursday after a US navy "towed pinger locator" picked up audio signals in the area, sparking hopes that the plane's black box was in the area.

Australian vessel Ocean Shield picked up four acoustic signals in the area, twice over the weekend and twice on Tuesday.

Speaking after the latest possible signal was detected, retired Air Chief Marshal Angus Houston, who is leading search efforts, said: "The acoustic data will require further analysis overnight but shows potential of being from a man-made source."

Media playback is unsupported on your device Media caption Hishammuddin Hussein: "I know there will be answers - I know we will find the plane - it's just a matter of when"

Up to 14 planes and 13 ships are involved in Thursday's search, scouring an area of 57,923 sq km (22 300 sq miles), around 2,280km (1,400 miles) north-west of Perth. It is the smallest designated area in the hunt to date.

Planes have dropped buoys equipped with hydrophone listening devices into the water to help pick up signals.

The batteries on the black box only last about a month, so teams need to work quickly to track the audio signals before they stop broadcasting.

'Nothing to hide'

Malaysia's acting transport minister has defended the investigation in an interview for BBC News, his first with a major Western broadcaster.

Hishammuddin Hussein said Malaysia had "nothing to hide", and he was "cautious" over the audio signals picked up by search teams.

"We've been following all sorts of leads from the South China Sea to the Straits of Malacca to the Andaman Sea," he said. "We have to be cautious because the families' emotions are still very raw and I've been through this rollercoaster ride."

MH370 - Facts at a glance 8 March: Malaysia Airlines Kuala Lumpur-Beijing flight carrying 239 people disappears

Malaysia Airlines Kuala Lumpur-Beijing flight carrying 239 people disappears Plane's transponder, which communicates with ground radar, was switched off as it left Malaysian airspace

Satellite 'pings' indicate plane was still flying seven hours after satellite contact was lost

24 March: Based on new calculations, Malaysian PM says "beyond reasonable doubt" that plane crashed in southern Indian Ocean with no survivors What we know The search for flight MH370

Malaysia has come under criticism for its handling of the search, with families of the passengers on the plane accusing the authorities of a lack of transparency.

The investigation came under further scrutiny after it emerged that the final words from the plane were "good night Malaysian three seven zero", and not "all right, good night", as previously reported by the government.

However, Hishammuddin Hussein defended his handling of the search, saying the transcript had been released and the discrepancy in the words didn't "really matter".

"We have formed the committees, international experts are on board, we've got panels of inquiries [on the search]," he said. "Malaysia has got nothing to hide."

He added that the full cost of the search for the plane, and which countries would bear the cost, were not yet clear, but that the search cost was "peanuts" compared to the costs of other international crises.

"How much is Ukraine costing everybody?" he asked. "How much has it been for Syria and it's still unfolding? How much does it cost the people of Egypt, Tunisia, Libya, Iraq? Not only in dollars and cents but in lives. Here it is peanuts."

Officials say satellite data show the plane, which was flying from Kuala Lumpur to Beijing, ended up in the southern Indian Ocean, far from its original flight path.

Investigators still do not know why MH370 strayed so far off course, after disappearing over the South China Sea between Malaysia and Vietnam.

The backgrounds of both passengers and crew have been scrutinised as officials consider hijacking, sabotage, pilot action or mechanical failure as possible causes.