An independent commission investigating the US government's anti-terror policies before the September 11, 2001 attack on Tuesday questioned military and diplomatic leaders of the Clinton and Bush administration.

Among those who testified were Secretary of State Colin Powell, his predecessor Madeleine Albright, Secretary of Defence Donald Rumsfeld and his predecessor William Cohen.

They all said that until 9/11, there was not enough support -- either domestically or internationally -- to send US troops into Afghanistan to capture or kill Osama bin Laden and his support.

"It would have been very hard, pre 9/11, to have persuaded anybody that an invasion of Afghanistan was appropriate," said Albright. "I think it did take the megashock, unfortunately, of 9/11, to make people understand the considerable threat."

Rumsfeld told commissioners there was no indication that something like 9/11 was going to happen. "I knew of no intelligence during the six-plus months leading up to September 11 to indicate terrorists would hijack commercial airlines, use them as missiles to fly into the Pentagon or the World Trade Center towers," he said.

"Second, even if bin Laden had been captured or killed in the weeks before 9/11, no-one I know believes it would have prevented 9/11," he added.

"Rooting out and dealing with terrorist enemies is tough. It will require that we think very differently."