The United States Defence Secretary, Donald Rumsfeld, says that the US cannot afford to wait for conclusive proof of Saddam Hussein's weapons programs before it attacks Iraq.
He equated the reluctance of America's allies to get involved with the appeasement of Nazi Germany.
His most outspoken remarks on Iraq to date appeared to be a deliberate move by the Bush Administration to ratchet up the anti-Saddam rhetoric in the face of scepticism at home and abroad.
Speaking of Nazi Germany, Mr Rumsfeld told Fox News on Tuesday: "Think of all the countries that said, 'Well, we don't have enough evidence'.
"I mean Mein Kampf had been written. Hitler had indicated what he intended to do. Maybe he won't attack us. Maybe he won't do this or that. Well, there were millions of people dead because of the miscalculations."
He said the risk of a terrorist attack with a biological, chemical or nuclear weapon was so high, that the US could not wait for more evidence before acting.
In another development, intelligence officials on Tuesday said at least a handful of senior members of al-Qaeda had taken refuge in Iraq.
Iraq has often been cited by US officials as a haven for al-Qaeda fighters who have fled the US military campaign in Afghanistan.
"There are some names you'd recognise," a defence official said.
The reports of a more significant al-Qaeda presence in Iraq come as the Pentagon plans for a possible invasion. They also serve President George Bush's arguments for toppling Saddam.
A senior US intelligence official said there was no evidence that Saddam had formally "welcomed in or sheltered" the terrorists.
"They are not the official guests of the Government," another official said. They were largely still "on the run".
But Mr Rumsfeld scoffed at the notion that al-Qaeda's members were hiding in Iraq without the full knowledge or protection of the Government.
Iraq's deputy prime minister, Tariq Aziz, said in an interview with CBS News on Tuesday that members of al-Qaeda were operating in the northern part of Iraq and were not under the control of the Iraqi Government.
They were operating under the Kurdish opposition leader, Jallal Tallabani, "an ally of Mr. Rumsfeld".
Meanwhile, General Wesley Clark, NATO's commander during the Kosovo war, has joined the growing ranks of US elder statesmen, including prominent Republicans and former US military commanders, in urging caution about attacking Iraq.
General Clark said on Tuesday that privately even the "hawks" in the US Government acknowledged that Iraq was no threat to America.