While claiming 'excellent progress' on the fourth day of the US-led war on Iraq,  Defence Secretary Donald Rumsfeld on Sunday conceded that some US troops were missing and may have been captured by Iraq.

Qatar-based television channel Al Jazeera aired what it said were images of US soldiers taken prisoners by Iraq.

But a grim-faced Rumsfeld dismissed the contents of the broadcast.

"It seems to me that showing a few pictures on the screen, not knowing who they are and being communicated by Al Jazeera, which is not a perfect instrument of communication, obviously is part of Iraqi propaganda," he told CBS television's Face the Nation programme.

Earlier, he told NBC TV's Meet the Press programme that 'some American soldiers are missing in the fighting and possibly being held as prisoners'.

He claimed thousands of Iraqi troops have surrendered 'but there are pockets of resistance and how long the war will last and how many casualties the US and its allies will suffer no one can say'.

Rumsfeld insisted that the 'outcome is clear: It will end with Saddam Hussein's regime gone and the United States will be a safer place'.

About rumours that Saddam Hussein may be dead or injured, Rumsfeld said: "We have to assume he is alive and well".

It has also to be assumed, he said, that the Iraqi president will have many methods of communication with his troops -- from electronic to couriers -- although he claimed the US was getting reports, by watching the Iraqi behaviour, that there is some confusion.

Asked how long the regime change will take, Rumsfeld said it is self-evident that the present regime is already not in control of large parts of the country.

"The US, Australian, British and Polish forces on the ground are doing a wonderful job and so far they have been pretty much on schedule," he said but added it is possible that as the forces move from the south, north and west, the degree of resistance could increase.

Describing Saddam Hussein as 'tough' and 'a survivor', Rumsfeld warned that there may be tough days ahead.

Talking to CBS, Rumsfeld claimed Republican Guards (elite forces of Iraq) in selected places are in discussions to surrender.

"The US goal is to have this done with the minimum loss of life on the coalition side and on the Iraqi side."

If the Iraqi military will "act with honour and stop supporting the regime, help liberate the Iraqi people and help find the weapons of mass destruction and destroy them, the whole world will be better off," he said.

He expressed disagreement at Turkey's desire to have its forces in northern Iraq saying, "We don't feel it is appropriate or necessary for them, and to my knowledge they have not."

PTI