US Defence Secretary Mr Donald Rumsfeld outlined an apocalyptic experience for Iraq if it resisted US-led invasion forces, and instructed Iraqi soldiers to surrender and Iraqi civilians not to go to work.
The attack on Iraq would be of a "force and scope and scale beyond what has been seen before" warned Mr Rumsfeld and Iraqi soldiers had the option of dying for a doomed regime or of staying alive and playing a role in a "new and free Iraq".
A second round of US-led air attacks was launched on Baghdad as darkness fell there, but US military officials said this did not signal the start of the massive "shock and awe" air campaign the Pentagon has planned.
Sea-launched Tomahawk cruise missiles were fired from British and US ships at Special Republican Guard strongholds in Baghdad, according to defence officials.
Mr Rumsfeld disclosed that the US had hit a suspected "senior leadership compound" in the first US strikes on Baghdad at dawn on Thursday, and that US officials were trying to establish whether the pictures of Saddam Hussein shown later on Iraqi television had been taped before the US strike or were of a body double.
Standing beside him at a Pentagon briefing, the chief of the general staffs, Gen Richard Myers, looked furious when asked how he could reconcile his earlier statement that Saddam Hussein was not a target with the US attempt to kill him yesterday morning.
"Regime leadership, command and control is a legitimate target in any conflict and that is the target that was struck last night," he snapped back.
Gen Myers also warned, "We do not regard combat as an easy task. Warfare is dangerous. We will have casualties."
Mr Rumsfeld, the civil official heading the most high-tech assault in modern warfare, said that there was no need for a broader conflict in Iraq if the regime's leaders acted to save themselves by turning themselves in or leaving the country.
If Saddam Hussein and his generals, however, ordered the use of weapons of mass destruction those orders should not be followed, he warned.
"Do not follow orders to destroy dams or flood villages. . .or destroy oil," he said. These would be crimes against the Iraqi people. "See those orders for what they are - the last desperate gasp of a dying regime." Those who followed such orders would be found and punished and "would forfeit amnesty or leniency with respect to past actions," he said. "If you follow Saddam Hussein's orders you will share his fate. The choice is yours."
With the Pentagon now broadcasting in Arabic into Iraq, the US Defence Secretary instructed Iraqi soldiers to listen to the radio, where they would receive advice on how to demonstrate to advancing US forces that they did not intend to fight.
He added that the US had evidence from contacts in the regular Iraqi army and the Republican Guard that its personnel were increasingly aware Saddam Hussein would soon be gone.
Meanwhile, the second-ranking anti-terrorism official in President Bush's National Security Council has resigned, the second high-ranking White House official in the war on terrorism to quit this year. Mr Rand Beers resigned for personal reasons, a White House spokesman said.