And al Qaeda linked attacks have grown increasingly sophisticated and brazen.
For instance, this week, attackers hit a military checkpoint west of Mosul with a suicide car bombing. Gunmen then targeted ambulances carrying victims, police said.
In another example, fighters from the group carried out sophisticated, multipronged attacks on two prisons near Baghdad in July, setting hundreds of prisoners free, including high-ranking al Qaeda members, according to authorities.
The situation has grown dire enough to raise the specter of a renewed civil war there, according to many analysts and even the special representative of the U.N. secretary-general in Iraq, Nickolay Mladenov.
"Today, Iraq is riven by constant and worsening violence, and the prospect of deepening sectarianism casts a dark shadow over the country. These challenges -- both developmental and security -- threaten the very fabric of Iraqi society and test the extent of the nation's social cohesion," he said in a speech last week in Baghdad.
The situation next door in Syria, where civil war is raging, isn't helping Iraq's stability.
Not only are Kurdish officials having to find ways to deal with nearly 200,000 refugees who have sought shelter in relatively peaceful northern Iraq, the conflict is increasing militancy in the region.
"The war in Syria has become a magnet that attracts sectarian extremists and terrorists from various parts of the world and gathers them in our neighborhood, with many slipping across our all-too-porous borders," al-Maliki wrote in a New York Times opinion piece this week.
Although Iraq is technically neutral on Syria's civil war, al-Maliki is widely seen as supportive of the county's president, Bashar al-Assad, for fear of what could happen should Sunni extremists linked to al Qaeda take control there.
"The civil war in neighboring Syria has exacerbated domestic tensions," the Global Centre for the Responsibility to Protect, a human rights group, recently wrote. "Many Sunni and Shia radicals have joined armed groups fighting in Syria, while Prime Minister Maliki is seen by some Iraqis as being overly sympathetic to President Bashar al-Assad's government and its Iranian allies."
Given such issues to deal with, it's no wonder al-Maliki is calling on Obama to seek more assistance to help combat terrorism and other security concerns.
Among other things, he's seeking military equipment and other aid to help bolster border security, combat terrorism and tackle other threats.
The U.S. plans to go ahead with delivery of F-16 fighter jets to Iraq next year, and a senior U.S. official who spoke to reporters on background said this week that in addition to weapons sales, greater intelligence-sharing is also likely in the cards.
"What we don't want the Iraqis to do is just take a security-centric approach to this," the official said.
"What that means is making sure they have information in terms of where people are located, where it's coming from, where the funding is coming from, and that's something we can do pretty effectively," the official continued. "So we're trying to help them now as best we can, and that's going to be a key topic of discussion over the course of the visit."
Although gains have been made to restore Iraq's economy after years of war, occupation and violence, crushing poverty remains pervasive, and the economy remains fragile.
Nearly 2 million Iraqis sometimes lack enough to eat, Mladenov said. Infant mortality remains high, as does illiteracy and unemployment.
And the violence threatens to derail the country's oil production, which drives much of its economy.
According to Iraq's Oil Ministry, exports fell to 62.1 million barrels in September, from a peak of 79 million barrels in April, when the worst of the violence began.
A continued slide could threaten the government's ability to pay for increased security and economic development efforts.
The oil sector provides more than 90 percent of government revenue and four-fifths of its foreign exchange earnings, according to the CIA.