THE 2007 troop "surge", in which President George Bush sent nearly 30,000 additional US combat forces to Iraq, was not the primary factor behind the steep drop in violence there, according to a book by Washington Post associate editor Bob Woodward.

Rather, Woodward reports, "groundbreaking" new covert techniques enabled US military and intelligence officials to locate and kill insurgent leaders and key individuals in extremist groups such as al-Qaeda in Iraq.

The War Within: A Secret White House History, 2006-2008 also says the Bush Administration has run an extensive spying operation on Prime Minister Nuri al-Maliki, his staff and others in the Iraqi Government.

"We know everything he says," says one of multiple sources Woodward cites about the practice in the book, which is scheduled for release on Monday.

The book is Woodward's fourth to examine the inner debates of the Bush Administration and its handling of the Iraq and Afghanistan wars.