WASHINGTON -- U.S. military leaders said Sunday they expect fighting in Iraq to intensify as coalition forces advance toward Baghdad, facing increased resistance from Saddam Hussein's troops and their possible use of chemical or biological weapons.
"There have to be tough days ahead," said Defense Secretary Donald H. Rumsfeld. "How long is not knowable. How many casualties is not knowable."
"The hardest part is yet to come," said Gen. Richard Myers, chairman of the Joint Chiefs of Staff.
Giving an overall upbeat assessment of the progress of the war to date, Myers said the Iraqis nonetheless "are not a beaten force ... The future will be a little bit tougher."
Rumsfeld said there is a possibility that as the coalition forces move from the south, north and west that "the degree of resistance could increase for a period."
"The potential for the use of weapons of mass destruction, it grows as we get closer to Baghdad," said Rumsfeld.
President Bush, returning to the White House from Camp David, said "this is just the beginning of a tough fight." His defense team earlier appeared on five morning talk shows.
The notes of caution came as a handful of American soldiers were taken prisoner, the United States accidentally shot down a British warplane and an American soldier attacked his own comrades with a grenade.
Rumsfeld said that in the end, the Iraqi military will surrender, but "how long it will take and when it will tip, I don't know."
"The closer we get to Baghdad, the greater the pressure, the more likely that they'll tip," he said.
Rumsfeld said various ploys used by the Iraqis won't work, such as writing messages on the roofs of some buildings saying that civilian "human shields" were inside.
The Iraqis also have used false surrenders, co-mingling their forces in civilian areas and disguising soldiers in civilian clothes.
Regardless of what Iraq does, "we are not going to be deterred at all," Rumsfeld said.
Rumsfeld noted that while Saddam can order the use of lethal weapons, it is up to his military to carry it out.
"We have focused extensively on the military people that he would have to persuade to do it, and let them know in no uncertain terms that they must not do it, and if they do do it, they will be hunted down and punished," Rumsfeld said.
The defense secretary said he had heard reports printed in the British press that Saddam was seriously injury and needed a blood transfusion, but Rumsfeld said Saddam's fate from the Wednesday night missile attack is uncertain.
Saying the Iraqi government has mingled its military installations with mosques, hospitals and schools, Rumsfeld said he would advise anyone "anywhere near" military facilities to leave.
While on one talk show, Rumsfeld watched for the first time the videotape of apparent American POWs. He said that if the footage was authentic, such humiliating treatment of captives violates international law. Appearing later on CNN, Rumsfeld said the American networks shouldn't air the tape.
Rumsfeld said that "sure" some things have gone wrong in the past five days, including the shooting down of the British plane. Myers said elaborate electronic procedures for identifying friendly aircraft "obviously ... didn't work."