BAGHDAD (AP) — 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 Shiite 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

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 the Levant 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.

The Islamic State’s Sunni militants have carved out a large fiefdom along the Iraqi-Syrian border and have long traveled 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 200 miles (320 kilometers) west of Baghdad, after killing some 30 Iraqi troops in daylong clashes Friday.

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 Shiite-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.

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 Shiite militias and Shiite volunteers to bolster his beleaguered security forces.