The reluctance of a majority of the Shia population to rise up and welcome the United States and British troops besieging Basra, Iraq's second largest city and the soft under belly of Saddam Hussein's regime, is turning out to be one of the biggest conundrums of the current campaign.

Only last week US and British military experts were predicting that Basra would fall 'within days'. The initial reactions of the men, women and children in the shanties on the outskirts of the city, who cheered and waved at the allied troops, seemed to be consistent with the forecasts.

But something changed and the cheery faces picked up by Western television crews have been replaced by sullen looks as coalition aircraft pound the city and its precincts in a continuing bid to flush out what is evolving into an Iraqi-guerilla resistance.

Even the tiny port of Umm Qasr, barely 20 miles from the Kuwaiti border, has proven to be a tough nut for the coalition to crush. Booby traps, bombs and grenade attacks have welcomed the foreign forces, who were told by their commanders they would be greeted by flowers and applause.

By all accounts Iraqi Deputy Prime Minister Tariq Aziz touched a chord in many Iraqis when he told Western journalists in Baghdad on Monday night, "Bush and Blair said they would be welcomed with music and flowers. They are indeed welcome to come to Baghdad and we will receive them with the best music they have ever heard and the finest flowers grown in Iraq - bullets."

While coalition intelligence experts may have misjudged the mood of the civilian population, Saddam's clever use of guerilla tactics has also forced the allies to be far more heavy-handed and cautious against the civilian population than they ever intended.

Cruise missile strikes on the outskirts of Basra and the use of Apache helicopters to fire missiles against guerilla hideouts have inevitably enraged the very people the coalition forces want on their side.

This was never part of the Allies plan, nor was the reaction of the local population, which has been turning its anger against the would-be liberators.

In Al Zubayr a British tank commander was shot dead -- the first UK combat casualty of the campaign -- when he climbed down from his turret in a futile bid to calm rioting civilians.

One theory is that he was the victim of local fanatics, or, as seems more likely, one of the crack shots from the volunteers who have joined the 'martyr battalions' in a bid to hit back at what they believe are the US and UK invaders of their country.

New plans are said to call for more accurate air strikes and to prepare for street by street fighting to secure Basra.

But if this is the level of resistance experienced in the first week of war, how much worse will it get when the coalition takes on Baghdad?