"In theory, any country that sees a strange blip is going to get fighter planes up to have a look," he said. "And if those fighter planes can't make head or tail of what it is, they will shoot it down."
Najib said search efforts in the South China Sea, where the plane first lost contact, had ended.
Two-thirds of the plane's 227 passengers were Chinese, and China's government has been under pressure to give relatives firm news of the aircraft's fate.
In a stinging commentary on Saturday, the Chinese government's Xinhua News Agency said the Malaysian information was "painfully belated," resulting in wasted efforts and straining the nerves of relatives.
"Given today's technology, the delay smacks of either dereliction of duty or reluctance to share information in a full and timely manner," Xinhua said. "That would be intolerable."
