Islamic insurgents who swept through northern and central Iraq, inflicting humiliating defeats on government forces, met tough resistance Tuesday on the northeast approaches to the capital and officials said the advance had been halted.
Amid heavy fighting and accusations of a sectarian massacre of prisoners, the government said it had stopped fighters from the Islamic State of Iraq and Syria at Baqubah, a city 35 miles northeast of Baghdad that could offer a direct route to the capital.
Clashes in the last week have raised fear that Iraq could disintegrate and descend into civil war, much like the fighting that has gripped neighboring Syria for more than three years and Iraq itself under U.S. occupation after the 2003 invasion to oust Saddam Hussein.
President Obama is considering options that include the use of U.S. air power, but has said he will not reintroduce U.S. combat troops. The White House said he would meet Wednesday with the four top congressional leaders to discuss Iraq and other foreign policy issues.
If the Iraqi government can hold Baqubah, that could signal the limits of the reach of the Al Qaeda breakaway faction that is leading the antigovernment insurgency.
The battle for Baqubah appears to be the closest that the fighting has gotten to Baghdad. Insurgents last week overran the cities of Mosul and Tikrit, northwest of the capital, routing government forces. Their reclusive leader urged his Sunni Muslim fighters to continue on to Baghdad, and beyond to the heavily Shiite areas to the south.
But approaching the heavily defended capital would pose stiff new challenges. Both Mosul and Tikrit are largely Sunni enclaves where the fighters were viewed by many as liberators from the forces of the Shiite-led government of Prime Minister Nouri Maliki.
Iraq's Shiite majority rallied in 2008 to help defeat Al Qaeda-style groups. Reports of mass executions of Shiites and the stated goal of the Islamic State of Iraq and Syria, or ISIS, to target revered Shiite shrine cities south of Baghdad have prompted tens of thousands of Shiite men to sign up for pro-government militias.
The conflict illustrates the lack of stability and reconciliation in Iraq throughout the U.S. occupation and after the departure of the last U.S. combat troops in 2011. Many Shiites despised Hussein, a Sunni Muslim. But the government that replaced him has been widely accused of marginalizing Sunnis.
Reeling from its rout last week in the north, the Iraqi government on Tuesday dismissed a number of army commanders and vowed to prosecute deserters.
Baqubah, with a mixed population, is the capital of Diyala province, which borders Shiite Iran and is home to many Shiites and Kurds.
Some analysts have suggested that ISIS, despite its audacious vision of an Islamic caliphate in the heart of the Middle East, is thinly stretched across a vast, mostly desert swath of Iraq and Syria.
It has seized hundreds of millions of dollars in cash and gold, and U.S.-made military equipment. But Iraq's oil wealth is largely concentrated in the Shiite-dominated south and in the semiautonomous Kurdish area and adjacent zones to the north. Kurdish forces, viewed as among Iraq's most cohesive fighting units, have vowed to resist any attempt by the militants to advance into territory they claim.
An insurgent push toward the capital could also come from Sunni areas to the west or northwest, where Sunni militants have made substantial gains dating to last year.
But ISIS and related groups are certain to meet fierce resistance once they leave Sunni-dominated areas. Despite their recent setbacks in the north, the Iraqi army and allied militias remain an imposing force with access to U.S. hardware and considerable aid from Iran. Some analysts are skeptical that the insurgents can advance much beyond zones of core Sunni support.
"ISIS has picked a fight it can't win," Joshua Landis, director of the Center for Middle East Studies at the University Oklahoma, wrote this week in a blog post. "I doubt ISIS will get a foothold in Baghdad."
Alternately, Sunni insurgents could work to destabilize the government through a campaign of car bombs, assassinations and guerrilla attacks, a familiar tactic in Iraq.
Battle-hardened militants may also use equipment and funds seized in their offensive to consolidate control in Sunni areas outside the capital and reinforce their efforts in Syria, where they face two enemies — the government of President Bashar Assad and other Syrian rebel factions.
In Iraq, many fear a renewed period of sectarian slaughter. Reports of retaliatory killings have already been circulating in the capital. A car bomb blast Tuesday killed at least 10 in Baghdad's Sadr City, a Shiite district, news agencies reported.
There were conflicting versions about the reported deaths of dozens of prisoners at a jail in Baqubah. Some pro-opposition groups blamed the government for a mass execution of Sunni prisoners, while authorities blamed attacking insurgents. Neither account could be independently verified.
Clashes also continued in Tall Afar, an ethnically diverse town 240 miles northwest of Baghdad in Nineveh province, a day after government officials and armed groups made conflicting assertions about who controlled the area.
Pro-government activists reported the establishment of an aerial supply bridge in which army and police units and members of Shiite militias would ferry soldiers and weapons to loyalist forces.
Army and police units in Mosul abandoned their posts and equipment last week with little resistance. That stunning development led to a string of similar capitulations across wide swaths of Sunni-dominated areas of Iraq, where some residents welcomed the Islamist fighters as "liberators" and "revolutionaries." Hundreds of thousands of others fled.
Maliki, stunned by what he termed "a black conspiracy" that will be "dyed by the blood of the traitors," launched a call for the formation of local militias, enlisting the help of prominent religious leaders, including Grand Ayatollah Ali Sistani, Iraq's preeminent Shiite cleric.
In an indication of how Iraq, like Syria, may become a proxy battlefield, the Iraqi prime minister lashed out at Saudi Arabia for what he called its support of Iraqi insurgents. Saudi Arabia, the major Persian Gulf Sunni power, is an archrival of Shiite Iran, which supports Maliki's government.
The United States and its allies have urged the Shiite-led Iraqi government to reach out to Sunnis. But instead, attitudes appear to be hardening.
U.N. Secretary-General Ban Ki-moon said Tuesday that he had urged Maliki and other Iraqi leaders to focus on national unity to prevent the disintegration of the country.
"There is a real risk of further sectarian violence on a massive scale, within Iraq and beyond its borders," he said.