WASHINGTON, March 24: US President George Bush's administration was forced to admit that the United States is still vulnerable to terrorist attacks two-and-a-half years after the Sept 11 attacks.

Government officials under Mr Bush and his predecessor, Bill Clinton, made the admission on Tuesday to an independent inquiry into the Sept 11, 2001, attacks.

Grilled by Republican and Democratic members of the independent commission, Bush officials acknowledged it was impossible to provide foolproof security to US citizens. "We're still vulnerable," Secretary of State Colin Powell told the panel.

In a nation as large and relatively open as the United States, he said: "We can't shut down our openness. We cannot be so afraid that we don't let anybody into our country."

"We should accept that, and we'll always be vulnerable as long as we are a free and open society," he added. Defense Secretary Donald Rumsfeld declined to link the absence of terrorist attacks on US soil since Sept 11, 2001, to the success of Mr Bush's declared "war on terrorism".

"As a former pilot, one of the things you always did was you never talked about the fact there hadn't been a flight accident for a long time," Mr Rumsfeld told the panel. "That's true. And with good reason. You start doing that, and something happens," he added.

"The fact is, a terrorist can attack any time, any place, using any technique. And we can't defend everywhere at every moment against every technique," Mr Rumsfeld said.

"We could have a terrorist attack anywhere in the world tomorrow. And we have to recognize that. This is a tough business we're in. And it is difficult. And it's challenging," the defense secretary added.

Despite the danger, he said, the United States has strengthened security in general around the country. Airports, railway lines, port facilities, bridges, dams, nuclear plants and some public places are now safer.

Mr Rumsfeld said the positive aspects of the "fight against terrorism" were the enhanced security measures and the coalition of 90 countries committed to sharing information on terrorists, tracking down their financial networks and preventing terrorists from entering their territory.

"But everything is harder. Everything is more difficult today. It's tougher to recruit, train, it's tougher to retain. It's tougher to finance. It's tougher to move things. It's tougher to communicate with each other for those folks," Mr Rumsfeld said.

The Commission on Terrorist Attacks Upon the United States, which began its hearings on Tuesday, has questioned more than 1,000 people in the past 16 months and reviewed some two million pages of documents. The panel's interim report said the Clinton and Bush administrations had failed to properly gauge the threat Al Qaeda presented. -AFP