Sunni insurgents led by an al-Qaida breakaway group expanded their offensive in a volatile western province on Saturday, capturing three strategic towns and the first border crossing with Syria to fall on the Iraqi side.

It's the latest blow against Prime Minister Nouri al-Maliki, who is fighting for his political life even as forces beyond his control are pushing the country toward a sectarian showdown.

In a reflection of the bitter divide, thousands of heavily armed Shia militiamen — eager to take on the Sunni insurgents — marched through Iraqi cities in military-style parades on streets where many of them battled U.S. forces a half decade ago

A burnt vehicle belonging to Iraqi security forces is left on a road Saturday in the town of Sulaiman Pek in northern Iraq. Sunni ISIS fighters have seized a border post on the Iraq-Syria frontier, smashing a line drawn by colonial powers a century ago. (Yahya Ahmad/Reuters) The towns of Qaim, Rawah and Anah are the first territory seized in predominantly Sunni Anbar province, west of Baghdad, since fighters from the Islamic State of Iraq and Syria (ISIS) group overran the city of Fallujah and parts of the provincial capital of Ramadi earlier this year.

The capture of Rawah on the Euphrates River and the nearby town of Anah appeared to be part of march toward a key dam in the city of Haditha, which was built in 1986 and has a hydraulic power station that produces some 1,000 megawatts. Destruction of the dam would adversely impact the country's electrical grid and cause major flooding.

Iraqi military officials said more than 2,000 troops were quickly dispatched to the site of the dam to protect it against a possible attack by the Sunni militants. They spoke on condition of anonymity because they were not authorized to speak to the media.

Rawah's mayor, Hussein Ali al-Aujail, said the militants ransacked the town's government offices and forced local army and police forces to pull out. Rawah and Anah had remained under government control since nearby Fallujah fell to the Sunni militants in January.

Border crossing control for ISIS

The Islamic State's Sunni militants have carved out a large fiefdom along the Iraqi-Syrian border and have long travelled back and forth with ease, but control over crossings like that one in Qaim allows them to more easily move weapons and heavy equipment to different battlefields. Syrian rebels already have seized the facilities on the Syrian side of the border and several other posts in areas under their control.

Police and army officials said Saturday that the Sunni insurgents seized Qaim and its crossing, about 320 kilometres west of Baghdad, after killing some 30 Iraqi troops in daylong clashes Friday.

Mehdi Army fighters loyal to Shia cleric Moqtada al-Sadr take part during a parade in Baghdad's Sadr city on Saturday. (Ahmed Saad/Reuters) The officials, who spoke on condition of anonymity because they were not authorized to talk to journalists, said people were now crossing back and forth freely.

Chief military spokesman Lt. Gen. Qassim al-Moussawi acknowledged Qaim's fall, telling journalists that troops aided by local tribesmen sought to clear the city of "terrorists."

The vast Anbar province stretches from the western edges of Baghdad all the way to Jordan and Syria to the northwest. The fighting in Anbar has greatly disrupted use of the highway linking Baghdad to the Jordanian border, a key artery for goods and passengers.

Al-Maliki's Shia-dominated government has struggled to push back against Islamic extremists and allied Sunni militants who have seized large swaths of the country's north since taking control of the second-largest city of Mosul on June 10 as Iraqi government forces melted away.

Shia militias parade streets

The prime minister, who has led the country since 2006 and has not yet secured a third term after recent parliamentary elections, also has increasingly turned to Iranian-backed Shia militias and Shia volunteers to bolster his beleaguered security forces.

Members of the Iraqi Special Operations Forces take their positions during clashes with the al Qaeda-linked Islamic State of Iraq and Syria (ISIS) in the city of Ramadi on Thursday. (Reuters) Reporting from Erbil, CBC's Nahlah Ayed said Saturday that over the last few days, there has been a call for volunteers who are willing to contribute to the fight to gather outside Baghdad.

"Today, it has been a show of force by one of the militias marching through Baghdad with flags and uniforms on," says Ayed. "It has been reconstituted over the last little while [that] a show of force raises the tension and certainly raises the sectarian violence, not just in Baghdad, but in the rest of the country."

The parades in Baghdad and other mainly cities in the mainly Shia south revealed the depth and diversity of the militia's arsenal, from field artillery and missiles to multiple rocket launchers and heavy machine guns, adding a new layer to mounting evidence that Iraq is inching closer to a religious war between Sunnis and Shias.

Al-Maliki has come under growing pressure to reach out to disaffected Kurds and Sunnis, with many blaming his failure to promote reconciliation that led to the country's worst crisis since the U.S. military withdrew its forces nearly three years ago.

In Baghdad, about 20,000 militiamen loyal to anti-U.S. Shia cleric Muqtada al-Sadr, many in military fatigues and even some wearing red berets, white gloves and combat helmets, marched through the sprawling Shia Sadr City district, which saw some of the worst fighting between Shia militias and U.S. soldiers before a cease-fire was reached in 2008 hat helped stem the sectarian bloodshed that was pushing the country to the brink of civil war.

Similar parades took place in the southern cities of Amarah and Basra, both strongholds of al-Sadr supporters.

Grand Ayatollah Ali al-Sistani, the most respected voice for Iraq's Shia majority, on Friday joined calls for al-Maliki to reach out to the Kurdish and Sunni minorities a day after U.S. President Barack Obama challenged him to create a leadership representative of all Iraqis.

Al-Sistani normally stays above the political fray, and his comments, delivered through a representative, could ultimately seal al-Maliki's fate.

Al-Maliki's State of Law bloc won the most seats in the April vote, but his hopes to retain his job have been thrown into doubt, with rivals challenging him from within the broader Shia alliance. In order to govern, his bloc, which won 92 seats, must first form a majority coalition in the new 328-seat legislature, which must meet by June 30.

If al-Maliki were to relinquish his post now, according to the constitution, the president, Jalal Talabani, a Kurd, would assume the job until a new prime minister is elected. But the ailing Talabani has been in Germany for treatment since 2012, so his deputy, Khudeir al-Khuzaie, a Shia, would step in for him.

U.S. back in the fray

The U.S., meanwhile, has been drawn back into the conflict with so much at stake. Obama announced Thursday he was deploying up to 300 military advisers to help quell the insurgency. They join some 275 troops in and around Iraq to provide security and support for the U.S. Embassy and other American interests.

Obama has been adamant that U.S. troops would not be returning to combat, but has said he could approve "targeted and precise" strikes requested by Baghdad.

Manned and unmanned U.S. aircraft are now flying over Iraq 24 hours a day on intelligence missions, U.S. officials say.

Iraq enjoyed several years of relative calm before violence spiked a year ago after al-Maliki moved to crush a Sunni protest movement against what the minority sect claimed was discrimination and abuse at the hands of his government and security forces.

Meanwhile, on Saturday four separate explosions killed 10 people, including two policemen, and wounded 22 in Baghdad, according to police and hospital officials. And in an incident harkening back to the peak days of sectarian killings in 2006 and 2007, two bodies, presumably of Sunnis, were found riddled with bullets in Baghdad's Shia district of Zafaraniyah, police and morgue officials said.

All officials spoke on condition of anonymity because they were not authorized to speak to journalists.