Malaysian Prime Minister Najib Razak has admitted the military did track a "civilian aircraft" entering their airspace at the time MH370 lost contact with ground control - but it failed to act as it "was not deemed to be hostile".

In an interview with CNN, Razak was pushed into explaining his country's role on the night when a reportedly junior radar military operator spotted the aircraft change its course towards the peninsula of Malaysia on 8 March.

It comes as a preliminary report into the disappearance of flight MH370 is due to be released next week.

Najib told CNN: "Now the military, the primary radar, has some capability. It tracked an aircraft which did a turn back, but they were not exactly sure whether it was MH370. What they were sure of was that the aircraft was not deemed to be hostile."

When asked if any planes were sent up on the night to investigate, Najib replied: "No, because - simply because it was deemed not to be hostile."

"Don't you find that troubling, that a civil aircraft can turn back, fly across the country, and nobody thinks to go up and have a look?" CNN's Richard Quest, asked.

"You see, coming back to my earlier statement was that they were not sure whether it was MH370," Najib said.

"Even more reason to go up and have a look," Quest pushed.

"They were not sure, but it behaved like a commercial airline," Najib replied.

His admission conflicts previous reports that military radar had not picked up any definite information that lead to speculation that the Boeing 777 had been flown deliberately low and close to the coastline to avoid being traced.

Najib also told CNN he found it bizarre when satellite data suggested the Beijing flight was suddenly found halfway across the Indian Ocean.

"To be honest, I found it hard to believe," said the Prime Minister.

"It's a bizarre scenario which none of us could have contemplated so that's why when I met the team...of foremost experts in aviation industry I asked them again and again 'are you sure?'.

"And their answer to me was we are as sure as we can possibly be."

The latest revelations will only further anger the families of the missing passengers who recently protested outside the Malaysian Embassy over the constant lack of information of the fate of their loved-ones.

"The ambassador kept saying he would come but he never showed," an elderly man told CNN.

"They're lying. They're lying to us."

The search for the missing aircraft has been hampered by a tropical cyclone, but crews will continue scouring the impact zone, 1,200 miles north west of Perth, until deployed to investigate new areas.