"(On) this day of reflection, I offer our deepest sympathies to their families," Bush said after a two-hour secured, video conference at the U.S. State Department. "I have vowed in the past, and I will vow so long as I'm president, to make sure that those lives were not lost in vain; that, in fact, there is a outcome that will merit the sacrifice that civilian and military alike have made ... "

Four U.S. soldiers died Sunday when a bomb exploded near their vehicle in Baghdad, bringing the number of U.S. military deaths in the Iraq war to 4,000.

Bush said the strategy moving forward would be to make sure victory is achieved and "therefore, America becomes more secure and these young democracies survive, and peace is more likely as we head into the 21st century."

Bush said he hoped the families of the deceased understand that "whether they were the first one who lost their life in Iraq or recently lost their lives in Iraq -- that every life is precious in our sight."