On Friday, two female suicide bombers blew themselves up near the gates of a Shiite Muslim shrine in Baghdad, killing 60 people. The attack followed two suicide bombs Thursday that killed more than 80 people.
The wave of violence in recent weeks, coming as US troops have begun preparing for withdrawal, threatens to bring Iraq back to the front burner, after months of increased security coupled with Obama's focus on Afghanistan had pushed it back.
Gen. David Petraeus, formerly the top US commander in Iraq and who now oversees both the wars there and in Afghanistan, warned lawmakers Friday that despite "substantial progress" in Iraq there remain lingering concerns. Al Qaeda in Iraq, as well as other groups, continue to pose a threat, he said.
"Numerous challenges still confront its leaders and its people," General Petraeus told a House panel. He said an Al Qaeda network that provides foreign fighters from Tunisia through Syria to Iraq has been "reactivated." Four of the most recent suicides were carried out by Tunisians, he said.
US forces are preparing to withdraw from Iraq over the next year and a half, with troops pulling out of the cities as early as June. Meanwhile, the Pentagon is preparing to send more than 21,000 additional troops to Afghanistan through this summer and fall.
While the Iraq withdrawal and the Afghanistan surge won't necessarily occur simultaneously, much of the deployment to Afghanistan is predicated on the draw down plan for Iraq. If Al Qaeda were to reemerge and pose a substantive challenge to Iraqi and US forces, Mr. Obama might have to reassess his thinking.
But some analysts also say there is no indication that the improved security in Iraq is being reversed.
"The enemy [insurgents] can't return to its former posture, nor is the situation likely to deteriorate quickly," says Kim Kagan, president of the Institute for the Study of War, an analysis group in Washington.
"But we need to remember that our forces are there for a reason," she adds.
The uptick in violence has not significantly affected US troops, yet. The number of American military personnel killed in Iraq has stayed under 20 per month since last October, according to the website icasualties.org. There have been 14 fatalities so far this month, compared with nine in March, according to the site.
The US has lost more than 4,200 troops in Iraq since 2003. Recently published numbers from the Associated Press put the Iraqis who've been killed in that time at about 87,000.
The 140,000-plus US forces currently in Iraq are supposed to leave by 2011, pending any new agreements with the government.
Resurgent violence is not the only reason to remain concerned about Iraq. Tensions among political parties, the return of displaced people, the release of detainees from American detention camps, and "new budget challenges," present additional factors for commanders on the ground, Petraeus told Friday's hearing.
At the same time, the US and Iraq are attempting to transition the so-called Sons of Iraq – the "neighborhood watch" groups of Sunnis and Shiites paid to provide security – from American to Iraqi control. Notwithstanding pledges from the government, it remains to be seen whether the largely Sunni group will be properly absorbed into Prime Minister Nouri al-Maliki's Shiite-led government.
But some things are going well. Generally, violence is down compared with 2006 and 2007. And the growing Iraqi security forces are carrying out the "vast majority" of security operations, Petraeus said.
"Despite the many challenges, the progress in Iraq, especially the steady development of the Iraqi security forces, has enabled the continued transition of security responsibility to Iraqi elements further reductions of coalition forces, and the steady withdrawal of our units from urban areas," said Petraeus.
"Iraq, now, is more of a Lebanon-like model," says Fawaz Gerges, a professor of Middle Eastern studies at Sarah Lawrence College in Bronxville, N.Y. He says it is a sectarian-based society still lacking in a unified national government, with a 50-50 chance of returning to a deeper conflict.
"Iraq remains a highly precarious society and, yes, violence has decreased," he says. "But all the elements are there for an escalation to a low-intensity conflict."
• Monitor correspondent Tom A. Peter contributed to this report.