They are also retracing every piece of cargo that was loaded on to the Boeing 777, including tonnes of mangosteens, a tropical Asian fruit with a leathery shell surrounding fragrant white flesh.

Malaysia’s top police officer Khalid Abu Bakar said the plane’s food caterers were being scrutinised in an investigation that has so far failed to uncover any significant leads into the disappearance of the plane with 239 people on board on March 8.

Inspector-General Khalid said every possible angle had to be investigated to rule out sabotage.

“For example when we knew there was a load of mangosteens on board we had to find out where the mangosteens came from,” he said. “We tracked down who plucked the fruits, who packed them and shipped them out, who put them on the plane.”

Inspector-General Khalid said investigators in China tracked down who was buying the fruit and for how much.

“Imagine how many people we must interview and that was just the mangosteens,” he said.

Police have refused to publicly release the plane’s cargo manifest but it is known to include a consignment of lithium-ion batteries that have previously been blamed for causing fires on aircraft. Malaysia Airlines claims the batteries are not dangerous as long as they are packed to international standards.

Meanwhile, China's ambassador in Kuala Lumpur Huang Huikang has defended Malaysia’s handling of the plane’s disappearance, denying allegations of any cover-up.

“There were weaknesses in the co-ordination between different departments and contradictory statements were given,” Mr Huang said. “They need to be improved in future efforts. But in the face of such a rare and immense disaster, no one can perform perfectly,” he said.

Mr Huang accused Western media of playing a disgraceful role.

“They have published false news, stoked conflict and even spread rumours,” he said. “These could provoke the frail spirits of the next of kin and damage the good relations between Malaysia and China. We strongly oppose this.”

-SMH