The US deputy defence minister, Paul Wolfowitz, has warned his Nato allies of future attacks by "terrorists" armed with weapons of mass destruction.
Wolfowitz, who spoke at a meeting of Nato defence ministers in Brussels, told his allies that there was "an alarming coincidence between those states that harbour international terrorists and those that have active weapons of mass destruction programmes."
He did not single out any state by name, but Washington considers Iran, Iraq, Syria and Libya among alleged state sponsors of terrorism and believes some of them could be developing nuclear or biological weapons.
Regarding collective military action, Wolfowitz said the US was seeking targeted help from individual allies in its "war against terrorism", however, it does not envisage collective Nato military action.
At the meeting the Nato ministers also praised the US for taking a long-term approach to responding to the September 11 attacks, which left about 7,000 people missing or dead.
US defence minister Donald Rumsfeld, who stayed in Washington to formulate the United States' response to the terrorist attacks, said on Tuesday the US will not launch a massive D-Day-type invasion, but is preparing instead for a long fight.
As part of that fight, the House of Representatives has approved a defence-spending bill worth $344 billion, which shifts $400 million from the country's missile defence budget so it can be used to battle terrorism.
The money will be used to beef up intelligence, domestic defence and crisis response programmes, but must still be voted on by the Senate.
Meanwhile, the US is continuing its military build-up - codenamed "Operation Enduring Freedom" - in apparent preparation for a strike on Afghanistan's Taliban rulers, who have refused to hand over fugitive militant leader Osama bin Laden.
He is the prime US suspect in the attacks on the World Trade Center in New York and the Pentagon, which are thought to have killed nearly 7,000 people.
A key element of the US operation is the building up of international support for its "war against terrorism". On Tuesday, Saudi Arabia bowed to US pressure and announced it had cut ties with the Taliban, leaving Pakistan as the only country which still has diplomatic relations with Kabul.
United Nations concerns about the plight of ordinary Afghans have been highlighted by the secretary general, Kofi Annan, who warned Afghanistan's Taliban rulers that the country was heading for a humanitarian crisis.
His comments came after international humanitarian agencies who have been supplying food to millions of Afghans were evicted by the Taliban and their offices seized. "The plight of the civilian Afghan population is indeed desperate," Annan said.
According to the United Nations High Commissioner for Refugees (UNHCR) the number of Afghan refugees fleeing to neighbouring countries could total more than 1.5 million.
Yousuf Hassan, a UNHCR spokesman, said nearly one million refugees could arrive in Pakistan, and tens of thousands of Afghans were already on the move inside the country.
swissinfo with agencies