As they spoke, the relentless violence killed at least 20 people, most of them in the capital. The U.S. military said a Marine was killed in combat Sunday.

Blair's official spokesman said at a news conference in Baghdad that he could not confirm the media report of a withdrawal within four years. Blair and al-Maliki also declined to set any deadline, with Blair saying withdrawal depends on the "readiness of the Iraqi troops and the situation on the ground."

On Jan. 31, a U.S. Embassy report found security "critical" in Anbar province, the Sunni-dominated region that includes war-torn Ramadi and Fallujah and is where many of the Sunni Arab-led insurgent groups are based.

The U.S. military said a U.S. Marine was killed in action in Anbar province Sunday. At least 2,457 U.S. service members have been killed since the war began, according to an AP count.

The security situation was considered serious in the provinces of Baghdad, Basra, Ninevah, Tamim, Salahuddin and Diyala - all of them religiously mixed between majority Shiites and minority Sunni Arabs. Those provinces include Iraq's three largest cities and the bulk of its oil wealth.

On May 6, a British military helicopter crashed - it apparently was shot down and all four soldiers aboard it died. Some Iraqis celebrated and in fighting that followed between British forces and Shiite gunmen, five Iraqis were killed.

Blair and al-Maliki discussed the situation in Basra on Monday and agreed to send a high-level Iraqi delegation soon to improve security and stability there.

In their joint statement, Blair and al-Maliki said the new government's plan is to have 325,000 members in Iraq's security forces by the end of the year, compared with 264,000 currently serving in the army and police forces.

Al-Maliki's new national unity government was sworn in Saturday and the prime minister pledged to used all means necessary, including "maximum force" against insurgents, "death squads" and some militias to restore stability and security.

Blair said Iraq's first full-term democratic government means there is no longer any justification for insurgents and that the best way for militants to get foreign troops to leave Iraq would be to lay down their arms.

"If the worry of people is the presence of the multinational forces, it is the violence that keeps us here. It is the peace that allows us to go," Blair said.

Separately, Iraq's Sunni Arab vice president said Iraqis had a legitimate right to resistance until coalition forces left Iraq. But Tariq al-Hashimi also called on insurgents to consider sitting down and talking to the United States since America was apparently seriously thinking about eventually withdrawing its forces.

Asked if Blair had spoken with Bush before traveling to Iraq, the prime minister's spokesman said the two leaders often talk regularly and "know each other's minds about Iraq."

The official, who spoke on condition of anonymity according to British government policy, also said Blair used his one-day visit to Baghdad to meet with U.S. Ambassador Zalmay Khalilzad and the top U.S. commander in Iraq, Gen. George Casey.

During the news conference, al-Maliki was asked whether the surge in sectarian violence in Iraq, which has prompted thousands of Iraqis to flee their homes, is a civil war.

"There are rebellious elements. There are gangs killing people. There are gangs that have used arms for political blackmailing or to achieve goals that have political dimensions," he said.

"But those groups have failed to ignite a civil war because the political, religious and social groups have faced this plot."

In Monday's deadliest attack, a roadside bomb killed four policemen in Musayyib, about 40 miles south of Baghdad, police said. Car bombs in two areas of the capital killed nine Iraqis and wounded 13, police said.

Elsewhere, officials said gunmen killed a police colonel in Samarra; an employee of a mobile phone company in Baqouba; the general director of the youth ministry in Baghdad; a Sunni Arab who headed the office that issues national ID cards to Iraqis in Kirkuk; and a former member of Saddam Hussein's Baath Party in Mosul.

Police found the bodies of two men - a police captain in the capital and a man in the Madain area, southeast of Baghdad, who had been shot in captivity.