"What we have for battle damage assessment right now is essentially a hole in the ground, a site of destruction where we wanted it to be, where we believe high value targets were," said Major General Stanley McChrystal, vice director of operations of the Joint Staff.

"We do not have a hard and fast assessment of what individual or individuals were on site," he said at a Pentagon press conference.

US officials said the building in the al Mansour residential area was targeted in response to intelligence that Saddam, his sons Uday and Qusay were meeting inside with senior Iraqi intelligence officials.

"We characterize the strike as being very, very effective," McChrystal said.

"In this case the 45 minutes time between when we received potential intelligence and actually put ordnance on the target is extraordinary," he said.

A B-1 bomber that was in the air over western Iraq was fed the coordinates and struck the building with four 2,000-pound, satellite guided bombs, two of them bunker busters, officials said.

Killing Saddam or his sons would be "militarily significant" because he commands the Special Republican Guard and irregular "death squads" that are the last major opposition to US forces moving into Baghdad, the army general said.

The Republican Guards were still receiving orders but were not following them or were incapable of carrying them out, he said.

Overshadowing the gains made by US forces in the Iraqi capital were mounting reports of civilian casualties, including the killing of three journalists and wounding of three others by US fire.

McChrystal and Pentagon spokeswoman Victoria Clarke offered condolences but defended the actions of a US tank crew that fired a round into a Baghdad hotel known to be full of international journalists.

"When they get into combat in the cities, which, from the beginning, we had specifically said would be dangerous and difficult, you put yourself in their position, they had the inherent right of self-defense," the general said.

"When they are fired at, they have not only the right to respond, they have the obligation to respond to protect the soldiers with them and to accomplish the mission at large," he said.

The US Central Command earlier said the tank fired after coming under fire, but journalists at the hotel said they heard no fire.

A cameraman for the Reuters television and a cameraman for Spain's Telecinco were killed by the blast, and three others from the British news agency were wounded.

In a separate incident, a US missile crashed into the offices of Al-Jazeera in downtown Baghdad, killing Tareq Ayub, a correspondent with the Arabic-language satellite channel, and wounding one of its cameramen.

"We continue to warn people, we continue to warn news organizations about the dangers," said Clarke.

"We've had conversations over the last couple of days, news organizations eager to get their people unilaterally into Baghdad. We are saying it is not a safe place, you should not be there," she said.

US forces, meanwhile, have encircled the Iraqi capital and were now able to maintain substantial US forces inside day or night, the general said.

"We are sitting in the center of the city with almost an armor brigade right now, which is extraordinary," McChrystal said.

The general said the US strategy was to subdivide the Iraqi capital to separate and weaken opposing Iraqi forces.

"Whenever we can operate through his capital, which is the core of the regime, we subdivide his capability to operate, we minimize or continue to degrade what command and control they have," he said.

"And as we convince the people that the regime is through, then we think that it becomes that much easier," he said.

"I think the end game is the end of the regime, and that's much closer than people thought it was," he said.

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