Stabilizing Iraq could take as long as a decade, the U.S. commander in Baghdad said.
"In fact, typically, I think historically, counterinsurgency operations have gone at least nine or 10 years," Gen. David Petraeus said Sunday. "The question is, of course, at what level."
His comments came as Secretary of State Condoleezza Rice prepared to meet with Iraqi foreign minister Hoshyar Zebari on Monday in Washington.
Petraeus said insurgents pushing back on newly aggressive coalition military forces have led to continued violence in Iraq, describing an ebb-and-flow of sectarian murders in Baghdad.
"The fact is that as we go on the offensive, the enemy is going to respond. That is what has happened," Petraeus said Sunday.
Petraeus also described a "stunning reversal" in the Anbar province, a former al-Qaida stronghold west of the city where tribes have begun to help fight the terror organization.
A Pentagon report released last week concluded that violence in Iraq edged higher during a four-month period between February and May - despite the U.S.-led security push in Baghdad.
The report also raised questions about Iraqi Prime Minister Nouri al-Maliki's ability to fulfill a pledge made in January to prohibit political interference in security operations and to allow no safe havens for sectarian militias.
Ryan Crocker, the U.S. ambassador in Baghdad, on Sunday called the situation in Iraq "a mixed picture, but certainly not a hopeless one." He noted frustrations among signs of progress, and cautioned against withdrawing troops too soon.
Also Sunday, the Senate's top Republican said that the Iraqis need to step up their own efforts as the U.S. scales back troops in the wake of rising violence in and around Baghdad. Sen. Mitch McConnell expressed disappointment with the Iraqi government's progress in stemming violence and said the U.S. presence there "will be different in the fall."
"I don't think we'll have the same level of troops, in all likelihood, that we have now," McConnell said. "The Iraqis will have to step up, not only on the political side, but on the military side to a greater extent. We're not there forever."
Congress is waiting for another progress report, due in September, on whether the increase in U.S. troops in Iraq has been successful.
In an interview in Newsweek magazine, al-Maliki avoided being drawn into the debate between the Bush administration and Congress. The U.S. "helped us by toppling the regime and accomplishing many steps of the political process but they still can leave," al-Maliki said. "If the consequences of staying are bigger than the consequences of leaving, they will leave."
Crocker said the Iraqis also are frustrated with their slow progress but are "very close" to agreement on a plan for managing the country's oil production and share resources.
Petraeus spoke on "Fox News Sunday." Crocker was interviewed from Baghdad on NBC's "Meet the Press." McConnell appeared on CBS' "Face the Nation."