Washington, Sep 8 (IANS): The biggest US mistake in the war against terrorism was to ignore Al Qaeda in Pakistan to invade Iraq after the September 2001 terror attacks and trusting then president Pervez Musharraf to "fight on our side", according to a former CIA analyst.

"This was the war that should have ended years ago," Bruce Riedel, now a foreign policy expert at the Brookings Institution, a Washington think tank, wrote in an article on how the US enabled Al Qaeda, the terror group behind the attack.

"The 9/11 attacks revealed a ruthless and agile enemy, one demanding unrelenting focus and smart. Instead, we made major errors," said the former Central Intelligence Agency analyst, who helped formulate President Barack Obama's Afghanistan-Pakistan policy.

Among the strategic mistakes made by the US, "The biggest was to ignore Al Qaeda in Pakistan to invade Iraq, which, at that point, posed no serious threat," Riedel said.

"The Bush administration underestimated Osama bin Laden's resilience, trusted the generals of Pakistan, and focused on the wrong battlefield."

Trusting then Pakistan president Pervez Musharraf "to fight on our side against bin Laden and the Taliban was another strategic failure," Riedel wrote.

"'Our man' in Islamabad turned out to be helping the Taliban regroup while bin Laden hid out in his front yard, living in plain sight of Pakistan's most elite military academy for years," he noted.

Now the death of Bin Laden and the revolutions sweeping the Middle East provide the United States with an opportunity to right its wrongs, he said but warnied "Pakistan remains the epicentre of the global jihad."

"Our enemy is still formidable, and the task isn't easy. But this time we have to get it right to avoid spending yet another decade fighting," Riedel said.