In an interview that cast doubt on the official investigation into the disappearance of the plane, Anwar Ibrahim said the country's "sophisticated" radar system would have identified it after it changed course and crossed back over Malaysia.
Mr Anwar, who knew the pilot of the Malaysia Airlines Boeing 777 that went missing in the early hours of March 8 during a flight from Kuala Lumpur to Beijing, called for an international committee to take over the Malaysian-led operation because "the integrity of the whole nation is at stake".
He indicated it was even possible that there was complicity by authorities on the ground in what happened to the plane and the 239 people on board.
In an interview, Mr Anwar said he had personally authorised the installation of "one of the most sophisticated radar" systems in the world, based near the South China Sea and covering Malaysia's mainland and east and west coastlines, when he was the country's finance minister in 1994.
The 66-year-old was once deputy prime minister in Malaysia's ruling coalition, which has governed the country since independence from Britain in 1957.
However, after falling out with the country's leaders, he was charged with sodomy, imprisoned twice and beaten in custody. He now leads a pro-democracy coalition of parties that lost last year's election despite winning more than 50pc of the popular vote amid allegations of corruption by the government.
Mr Anwar said it was "not only unacceptable but not possible, not feasible" that the plane had not been sighted by the Marconi radar immediately after it changed course.
The radar, he said, would have instantly detected the Boeing 777 as it travelled east to west across "at least four" Malaysian provinces.
Mr Anwar said it was "baffling" that the country's air force had "remained silent", and claimed that it "should take three minutes under SOP [standard operating procedure] for the air force planes to go. And there was no response."
He added: "We don't have the sophistication of the United States or Britain but still we have the capacity to protect our borders."
He said the families of the 153 Chinese victims among those on board were right to demand information from the Malaysian government, which had permitted a multi-national search operation to spend a week looking in what it must have known was the wrong place.
"Why didn't we alert the Chinese, the Vietnamese that the operation should cease in the South China Sea and let them spend millions on search and rescue in a place that they know fairly well cannot be the site of the plane?"
As hope fades of recovering the plane's black box before its batteries start to fail, which could be as early as Monday, Mr Anwar said it was "at the least, incompetence" on the part of the Malaysian government that it is still not known what happened to the plane, but was also a deliberate "intention to suppress key information". "Unfortunately the manner in which this was handled after the first few days was clearly suspect," he said.
"I believe the government knows more than us. They have the authority to instruct the air force or Malaysia Airlines. They are privy to most of these missing bits of information critical to our understanding of this mysterious disappearance."
Mr Anwar indicated it was a possibility that officials on the ground were complicit in what happened on the plane. But he later added that "the realm of possibilities is so vague, I mean, anything can have happened".