Washington — As the international community joins the United States in commemorating the terror attacks in 2001, the White House says threats to international security remain.

Speaking to journalists in Washington Monday, ahead of Tuesday's six year anniversary of the attacks on New York and the Pentagon, White House Press Secretary Tony Snow said those threats remained, and new ones had emerged.

"It is clear that after September 11th, the world was introduced to an entirely new series of security challenges that persist to this day.

"And al Qaeda remains a threat. Osama bin Laden, himself, no longer has freedom of movement or complete freedom of communication," Mr Snow told the press.

The press secretary said the Al Qaeda grouping, widely reputed to have masterminded the attacks on the World Trade Centre and the Pentagon, "remains committed" to attacking the U.S. and trying to destabilise the world's democratic nations.

"You saw the plots over the weekend in Denmark and Germany, both of which were aimed at Americans. And so it's important for us to remain vigilant, determined and steadfast in our support not merely of democracy and freedom, but also our resistance to those who have their own views, which is a view of a society that is bleak, totalitarian and bloodthirsty."

In reply to a question on public opinion and developments in Iraq, Mr Snow emphasised the importance of maintaining stability in theatres of conflict.

"We understand keenly the importance of public support.

"We also understand even more keenly what happens if the United States walks away and creates a vacuum in Iraq, which is a world that is far more dangerous, and in the long run will require a much greater expenditure of U.S. blood and treasure in trying to succeed in going after a terror network," said the press secretary.

He reiterated that the terror network continued to exist.

"It existed before September 11th, but it obviously was something that operated for the most part outside of public view and public awareness."

In the immediate aftermath of the attacks, South African President Thabo Mbeki used his address in the Debate of the 56th session of the United Nations General Assembly, to extend the nation's condolences and condemn the attacks.

"It is proper that we take advantage of this occasion once more to convey our condolences and deepest sympathy to the people and government of the United States at the immense loss of life and property imposed on them through a callous act of murder," President Mbeki said in New York, almost a month to the day, after the attacks.

"We extend the same sympathy to all other peoples who lost their citizens as a result of the colossal outrage of September 11."

Delivering the message on behalf of South Africa, the Non-Aligned Movement and the Commonwealth, Mr Mbeki at the time said, there could be no doubt that the people of the world had to unite in action to defeat terrorism.

"There can be no hesitation among any of us in the resolve to work together to ensure that those responsible for the heinous actions of September 11 are brought to justice," said Mr Mbeki.

"This is so not only because many nations lost their citizens on that terrible day, important as this is. It is so because terrorism has demonstrated that it has no respect for borders."

The President also viewed the attacks as an attack on democracies, and condemned the use of force to further political aims.

"September 11 emphasised the point that even as the democratic system of government is being consolidated throughout the world, even as we all work to sustain the possibility of a serious and meaningful global dialogue, there are some who are prepared to resort to force in pursuit of their goals," Mr Mbeki said.