Almost all U.S. soldiers will leave urban centers by June 30 under a security pact signed by Baghdad and Washington last year, and the whole force that invaded the country in 2003 must be gone by 2012.
"Don't lose heart if a breach of security occurs here or there," Maliki told leaders from the ethnic Turkmen community, reiterating a warning that insurgents were likely to try to take advantage of the U.S. pullback to launch more attacks.
Analysts warn there may also be a spike in violence by mainly Sunni Islamist insurgents, including al Qaeda, and other violent groups ahead of a parliamentary election next January.
Hours after Maliki spoke, a suicide bomber detonated a truck filled with explosives as worshippers left a Shi'ite Muslim mosque near the northern city of Kirkuk, a city contested by Arabs, Turkmen and Kurds and which sits over vast oil reserves.
Thirty-four people were killed, including women and children and about 150 civilians were wounded as dozens of clay homes in the area were flattened. Many people were feared trapped under the rubble, and the death toll was expected to rise.
There was chaos at Kirkuk's main Azadi Hospital, where ambulance sirens wailed as workers rushed blood-splattered civilians, including several children, into the wards.
Outside, security officials brandished assault rifles to stop traffic as pick-up trucks raced through the gates carrying more victims of the blast at the al-Rasul Mosque.
AL-QAEDA "USING NEW TACTICS"
Such attacks, including a string of devastating bomb blasts in April, have cast doubt on the ability of Iraqi security forces to take over after U.S. troops leave.
The bloodshed diminished significantly in May, and June has also seen fewer large-scale attacks.
It is not clear if that is due to the efforts of Iraqi police and soldiers, or if it means that insurgent groups, beaten back over the past two years in most of Iraq, now lack the organization and support to keep up the momentum.
Interior Ministry spokesman Major General Abdul-Karim Khalaf said al-Qaeda was resorting to paying people to fight for it. It had also turned to criminal activities to raise funds.
"It is a very important development. It shows al-Qaeda is starting to loss its impact," Khalaf told reporters. "Instead of recruiting people through faith or ideology, as it was in the past, now they are paying money to recruit people."
The sectarian bloodshed and insurgency unleashed by the invasion peaked in 2006/07, but volatile and ethnically mixed cities such as Mosul and Baquba remain dangerous.
Baghdad has also continued to see a steady stream of bombings and shootings and Kirkuk is viewed as a potential flashpoint for a broader conflict between Arabs and Kurds.
Maliki, a Shi'ite, said the start of the U.S. withdrawal was a "great victory" for Iraq over foreign occupation.
"I, and you, are sure that many don't want us to succeed and celebrate this victory," he said. "They are getting themselves ready to move in the dark to destabilize the situation, but we will be ready for them, God willing."
(Additional reporting by Mustafa Mahmoud in Kirkuk and Waleed Ibrahim in Baghdad; Writing by Michael Christie and Daniel Wallis; Editing by Louise Ireland)