Iraqi helicopters fired on a university campus in Tikrit on Friday to dislodge insurgents who overran the city in an onslaught that has given them control of most majority Sunni regions and brought them close to Baghdad, Reuters reported.
Tikrit, the hometown of former dictator Saddam Hussein, fell a fortnight ago to Sunnis led by fighters from the Islamic State in Iraq and the Levant (ISIL), which split from al Qaeda.
A rights group said analysis of photographs and satellite imagery "strongly indicate" that ISIL staged mass executions in Tikrit after seizing it on June 11 early in their offensive.
ISIL killed as many as 190 men in at least two locations over three days, Human Rights Watch said. Numbers may be much higher but the difficulty of locating bodies and getting to the area had prevented a full investigation, it added.
Iraqi forces launched an airborne assault on Tikrit on Thursday, flying commandos into a stadium in helicopters, at least one of which crashed after coming under fire from insurgents.
"My family and I left early this morning. We could hear gunfire and helicopters are striking the area," said Farhan Ibrahim Tamimi, a professor at the university who fled Tikrit for a nearby town.
Iraq's million-strong army, trained and equipped by the United States, largely evaporated in the north after the Sunni Muslim fighters led by ISIL launched their assault with the capture of the north's biggest city Mosul on June 10.
ISIL emerged after Abu Bakr al-Baghdadi, the leader a group then called the Islamic State in Iraq, defied the al Qaeda leadership by moving into neighboring Syria more than a year ago to join the civil war against President Bashar al-Assad.
The group is now fighting in both Iraq and Syria, seeking to erase the frontiers and create an Islamic caliphate stretching from the Mediterranean Sea to Iraq.
In Washington, President Barack Obama asked the U.S. Congress on Thursday to approve $500 million to train and equip moderate Syrian rebels, who have been largely upstaged by the more effective ISIL forces.
In Iraq, the fighters have been halted about an hour's drive north of Baghdad and on its western outskirts. However, they have pressed on with their advances in areas including the religiously mixed Diyala province and are consolidating their gains in northwestern Iraq.
Militants took control of six villages populated by the country's Shi'ite Shabak minority southeast of Mosul after clashing with Kurdish "peshmerga" forces who secure the area, according to a lawmaker and Shabak leader.
A new Iraqi parliament elected two months ago is set to meet on Tuesday to begin the process of forming a government that the United States and other countries hope will be inclusive enough to blunt the insurgency.
Fighters from ISIL - which says all Shi'ite Muslims are heretics who should be killed - have been helped in their advance by other, less radical groups who share their view that Sunnis have been persecuted under the Shi'ite-led government.
Washington hopes that armed Sunni tribal groups, which turned against al Qaeda during the U.S. "surge" offensive of 2006-2007, can again be persuaded to switch sides and back the government, provided that a new cabinet is more inclusive.
Prime Minister Nuri al-Maliki's Shi'ite-led State of Law coalition won the most seats in the April election but needs allies to form a cabinet.
Maliki confirmed this week that he would abide by the constitutional deadlines to set up a new government, after pressure from U.S. Secretary of State John Kerry, who flew to Baghdad for crisis talks earlier this week.
Under the official schedule, parliament will have 30 days from when it first meets on Tuesday to name a president and 15 days after that to name a prime minister.
In the past the process has dragged out, taking nine months to seat the government in 2010. Any delays would allow Maliki to continue to serve as caretaker.
The 64-year-old Shi'ite Islamist is fighting for his political life in the face of an assault that threatens to dismember his country. Sunni, Kurdish and rival Shi'ite groups have demanded he leave office, and some ruling party members have suggested he could be replaced with a less polarizing figure, although close allies say he has no plan to step aside.