US President George Bush is to send thousands more troops to Iraq to help secure Baghdad's streets as part of a new strategy to tackle the conflict.
Mr Bush said 80% of violence in Iraq happened within a 30-mile (48km) radius of the city and that the extra troops would help to secure the capital.
He said the situation in Iraq was unacceptable, and that responsibility for mistakes rested with him.
The troop announcement brought immediate criticism from Democrats.
Democratic Party leaders said Congress would give the proposals the "scrutiny our troops and the American people expect".
"We will demand answers to the tough questions that have not been asked or answered to date," they said.
Mr Bush said the vast majority of the new troops would be sent to Baghdad and would fight alongside Iraqi units to secure neighbourhoods from "terrorists and insurgents".
"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," he said.
But Mr Bush said the effort would succeed where previous operations had failed, because this time troop levels would be sufficient to hold areas that had been cleared.
He warned that his country's commitment to Iraq was "not open-ended", and that he expected the government in Baghdad to fulfil its own promises.
The key measures announced by Mr Bush include:
The Democrats have promised a non-binding vote in both houses of Congress on the strategy.
The US currently has 132,000 troops stationed in Iraq.
Mr Bush said some 4,000 troops would go to Anbar province.
Al-Qaeda was planning to seize control of the province, but local tribal leaders were starting to show willingness to fight them, the president said.
"As a result, our commanders believe we have an opportunity to deal a serious blow to the terrorists," he added.
Mr Bush also warned the Iraqi government to keep to its own commitments, mentioning Mr Maliki's pledge to crack down on "outlaws" from both sides of Iraq's sectarian divide, and the need for improvements to Iraq's basic services.
Iraq's territorial integrity also needed defending, Mr Bush said, and this meant interrupting the flow of support for insurgents from Iran and Syria.
Victory would not look like those won in previous wars - but failure in Iraq would be a disaster for the United States, he said.
Senior Democrats, whose party recently took control of both houses of Congress, were critical.
Senator Richard Durbin said the president was ignoring the advice of the former US commander in Iraq, Gen John Abizaid, that increasing troop numbers would prevent the Iraqis from taking more responsibility for their own future.
The BBC's James Coomarasamy in Washington says that many of the recommendations of the bipartisan Iraq Study Group were conspicuous by their absence.
Instead, for example, of calling for more diplomacy with Iran and Syria, Mr Bush pledged to seek out and destroy Iranian and Syrian networks which he said were equipping and training enemies of the US in Iraq.
James Carafano, a military adviser for the Iraq Study Group, notes Mr Bush's speech failed to discuss the risk involved in the new strategy.
"If anything, I think the president should have been more forthcoming in saying that, 'Look we can do this, it's worth trying to save this country and save this democracy... but we should realise that we can do all those things and we can still fail in Iraq'."