He said "massive amounts" of humanitarian aid would begin entering Iraq within 36 hours, and sternly urged Turkey not to send troops into northern Iraq.
Bush spoke as he returned to the White House from the Camp David presidential retreat. He said he had been briefed about a "potential capture" of US soldiers by Iraq and not all the details were clear.
"The POWs I expect to be treated humanely, just like we're treating the prisoners that we have captured humanely. If not, the people who mistreat the prisoners will be treated as war criminals," Bush said.
Iraqi television on Sunday showed video of at least four bodies, said to be US soldiers and five prisoners they said were Americans taken in a battle near the southern city of Nassiriya. US officials said the tape appeared to be authentic.
Iraq said it would respect the Geneva Convention guaranteeing humane treatment of prisoners.
Still early days
Bush said there had been progress in the war, but warned that it was still early.
"We're on course and we're making good progress," he said. "This is just the beginning of a tough fight...in terms of the overall strategy we're just in the beginning phases."
"I know that Saddam Hussein is losing control of his country," he said. He said "most of the South" was in the hands of US-led forces, despite resistance in some areas, and there was progress in western Iraq, where troops were seeking to take out Scud missile launch sites.
He appeared to rule out any additional offer of exile of Saddam, a possibility US officials had left open in the early hours after the expiration on Wednesday night of Bush's ultimatum for the Iraqi leader to leave Iraq or face war.
"He had his chance to go into exile...He chose not to go into exile," Bush said.
He said he was pleased southern Iraqi oilfields were safeguarded before they could be sabotaged. "At least in the south, they are secure," he said.
Bush said Ankara was well aware of a firm US policy against the sending of any Turkish troops into northern Iraq and said the US troop presence in the region had increased.
He said the United States was working with Kurdish populations in the region to prevent any incident which could spark a Turkish incursion.
Turkey is concerned about a potential rebellion by Iraqi Kurds that could also foment unrest among Kurds in Turkey.
The United States said about 1 600 British and US aircraft had flown nearly 6 000 sorties since the war began.
Iraqi television showed Saddam, whom US forces tried to kill in an air attack that began the war on Thursday, meeting military leaders he earlier thanked for staunch resistance.
About 280 000 US and British troops have been assembled for the war.
This is the first war the United States has fought since a national security strategy was announced last year that asserts Washington has the right to launch pre-emptive strikes on countries deemed a threat even before the United States itself is attacked.
- SAPA
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