The FBI is aiding the Malaysian government's search for a Malaysia Airlines jet missing for more than a week, the White House has confirmed.

The US investigators are believed to be helping the Malaysians examine a home flight simulator belonging to one of the pilots of flight MH370 for clues.

The pilot is said to have deleted some files from the computer simulator.

Teams from 26 countries are trying to find flight MH370, which went missing on 8 March with 239 people on board.

The flight was headed from Kuala Lumpur to Beijing.

On Wednesday, White House spokesman Jay Carney confirmed the FBI was assisting the investigation and said Malaysia was also speaking to US aviation and transport accident investigation agencies.

"We are finding that the level of cooperation with the Malaysian government is solid, and we are working closely with the Malaysians as well as our other international partners in this effort to find out what happened to the plane and why it happened," he said.

A US law enforcement official told Reuters the Malaysian officials gave the FBI access to data generated by both pilots including data from a hard drive attached to the captain's flight simulator and electronic media used by a co-pilot.

But the official stressed there was no guarantee the FBI analysis would lead to further clues.

Malaysian police chief Khalid Abu said some data was deleted on 3 February from the simulator found at Captain Zaharie Ahmad Shah's home and that investigators were trying to recover the deleted files.

The acting transport minister, Hishammuddin Hussein, stressed the captain should be considered innocent until proven guilty and that members of his family were co-operating with the investigation. Deleting files would not necessarily be suspicious, particularly if it were done to free up memory space.

The Malaysian authorities have said the evidence so far suggests the Boeing-777 was deliberately turned back across Malaysia to the Strait of Malacca with its communications systems disabled. They are unsure what happened next.

Investigators have identified two giant arcs of territory spanning the possible positions of the plane about seven hours after take-off.

This is based on its last faint signal to a satellite - an hourly "handshake'' broadcast even when communications are switched off. The arcs stretch up as far as Kazakhstan in central Asia and deep into the southern Indian Ocean west of Australia.

Investigators are considering the possibility of hijacking, sabotage, terrorism or issues related to the mental health of the pilots or anyone else on board.

Earlier on Wednesday, frustration with the lack of progress boiled over into chaotic scenes as Chinese relatives were dragged away from journalists in Kuala Lumpur, Malaysia's capital.

They were attempting to speak to Chinese journalists outside the daily press conference.

A BBC reporter was pushed away from the relatives, who were carrying banners criticising the handling of the case.

One of the relatives, a middle-aged woman, cried: "They give different messages every day! Where's the flight now? Find our relatives! Find the aircraft!"

The Malaysian government said later it regretted the scenes and ordered an investigation, saying "one can only imagine the anguish they are going through".