President Bush's new strategy on Iraq contained a commitment to increase US troop levels, an explanation for failures to date, and an expression that the Iraqi government must hold to its security commitments.
Mr Bush also pledged a renewed diplomatic initiative in the Middle East and said his secretary of state, Condoleezza Rice, would leave for the region today.
Here is an edited extract of Mr Bush's televised address:
"When I addressed you just over a year ago, nearly 12 million Iraqis had cast their ballots for a unified and democratic nation. The elections of 2005 were a stunning achievement. We thought that these elections would bring the Iraqis together, and that as we trained Iraqi security forces we could accomplish our mission with fewer American troops.
"But in 2006 the opposite happened. The violence in Iraq - particularly in Baghdad - overwhelmed the political gains the Iraqis had made. Al-Qaeda terrorists and Sunni insurgents recognised the mortal danger that Iraq's elections posed for their cause, and they responded with outrageous acts of murder aimed at innocent Iraqis.
"They blew up one of the holiest shrines in Shia Islam - the Golden Mosque of Samarra - in a calculated effort to provoke Iraq's Shia population to retaliate. Their strategy worked. Radical Shia elements, some supported by Iran, formed death squads. And the result was a vicious cycle of sectarian violence that continues today.
"The situation in Iraq is unacceptable to the American people - and it is unacceptable to me. Our troops in Iraq have fought bravely. They have done everything we have asked them to do. Where mistakes have been made, the responsibility rests with me.
"It is clear that we need to change our strategy in Iraq. So my national security team, military commanders, and diplomats conducted a comprehensive review . . . Failure in Iraq would be a disaster for the United States.
"The consequences of failure are clear: radical Islamic extremists would grow in strength and gain new recruits. They would be in a better position to topple moderate governments, create chaos in the region and use oil revenues to fund their ambitions.
"Iran would be emboldened in its pursuit of nuclear weapons. Our enemies would have a safe haven from which to plan and launch attacks on the American people. On September the 11th, 2001, we saw what a refuge for extremists on the other side of the world could bring to the streets of our own cities. For the safety of our people, America must succeed in Iraq.
"The most urgent priority for success in Iraq is security, especially in Baghdad. Eighty per cent of Iraq's sectarian violence occurs within 30 miles of the capital. This violence is splitting Baghdad into sectarian enclaves, and shaking the confidence of all Iraqis. Only Iraqis can end the sectarian violence and secure their people. And their government has put forward an aggressive plan to do it.
"Our past efforts to secure Baghdad failed for two principal reasons: there were not enough Iraqi and American troops to secure neighbourhoods that had been cleared of terrorists and insurgents. And there were too many restrictions on the troops we did have. Our military commanders reviewed the new Iraqi plan to ensure that it addressed these mistakes. They report that it does. They also report that this plan can work.
"Now let me explain the main elements of this effort: the Iraqi government will appoint a military commander and two deputy commanders for their capital. The Iraqi government will deploy Iraqi army and national police brigades across Baghdad's nine districts. When these forces are fully deployed, there will be 18 Iraqi army and national police brigades committed to this effort, along with local police. These Iraqi forces will operate from local police stations - conducting patrols and setting up checkpoints, and going door to door to gain the trust of Baghdad residents.
"This is a strong commitment. But for it to succeed, our commanders say the Iraqis will need our help. So America will change our strategy to help the Iraqis carry out their campaign to put down sectarian violence and bring security to the people of Baghdad. This will require increasing American force levels. So I've committed more than 20,000 additional American troops to Iraq. The vast majority of them - five brigades - will be deployed to Baghdad.
"These troops will work alongside Iraqi units and be embedded in their formations. Our troops will have a well-defined mission: to help Iraqis clear and secure neighbourhoods, to help them protect the local population, and to help ensure that the Iraqi forces left behind are capable of providing the security that Baghdad needs.
"Many . . . will ask why this effort will succeed when previous operations to secure Baghdad did not. Well, here are the differences: in earlier operations, Iraqi and American forces cleared many neighbourhoods of terrorists and insurgents, but when our forces moved on to other targets, the killers returned.
"This time, we'll have the force levels we need to hold the areas that have been cleared. In earlier operations, political and sectarian interference prevented Iraqi and American forces from going into neighbourhoods that are home to those fuelling the sectarian violence. This time, Iraqi and American forces will have a green light to enter those neighbourhoods - and prime minister Maliki has pledged that political or sectarian interference will not be tolerated.
"I've made it clear to the prime minister and Iraq's other leaders that America's commitment is not open-ended. If the Iraqi government does not follow through on its promises, it will lose the support of the American people - and it will lose the support of the Iraqi people. Now is the time to act . . .
"Over time, we can expect to see Iraqi troops chasing down murderers, fewer brazen acts of terror and growing trust and co-operation from Baghdad's residents. When this happens, daily life will improve, Iraqis will gain confidence in their leaders, and the government will have the breathing space it needs to make progress in other critical areas. Most of Iraq's Sunni and Shia want to live together in peace - and reducing the violence in Baghdad will help make reconciliation possible.
"A successful strategy for Iraq goes beyond military operations. Ordinary Iraqi citizens must see that military operations are accompanied by visible improvements in their neighbourhoods and communities.
"So America will hold the Iraqi government to the benchmarks it has announced . . ."