US President George W. Bush has told Americans that the o­nly way to limit the length and scope of combat in Iraq was to use decisive force.

After US and British aircraft unleashed the devastating firepower of missiles and bombs the Pentagon calls "shock and awe," Bush warned the Iraqi government, "This will not be a campaign of half measures."

Reuters reported that three days into war, Bush also cautioned against overconfidence given the apparent success of the mission and lack of serious resistance so far.

More difficult

"A campaign o­n harsh terrain in a vast country could be longer and more difficult than some have predicted," Bush said in his weekly radio address broadcast from Camp David where he is spending the first weekend of the war.

Foreign policy and military aides, including national security adviser Condoleezza Rice, Defense Secretary Donald Rumsfeld, CIA Director George Tenet and Secretary of State Colin Powell joined him at the presidential retreat 100 km from the White House.

Bush left Washington o­n Friday afternoon as US and British jets launched a major air assault o­n Baghdad and ground forces thrust deep into Iraqi territory toward the capital where Saddam's supporters were dug in.

In the private study off the Oval Office, Bush and his chief of staff, Andrew Card, watched some of the stunning television coverage of the attacks, which were still being broadcast worldwide as the family boarded the helicopter.

"I want Americans and all the world to know that coalition forces will make every effort to spare innocent civilians from harm," Bush said in the radio address recorded before he left the White House.