Iraq's Sunni militant groups have seized large part of a key city near the Syrian border after fierce clashes with Iraqi security forces on Saturday in Iraq's western province of Anbar, security sources said.

In Anbar province, Sunni militants, including those who are linked to the Islamic State in Iraq and Levant (ISIL), an al-Qaida offshoot, have taken control of most of the city of al-Qaim, some 330 km northwest of the capital Baghdad, after fierce clashes since the early hours of the day, a provincial police source told Xinhua on condition of anonymity.

The troops backed by allied tribesmen on Friday foiled an attack by the Sunni militants on the city, but the militants managed to seize large parts of the city earlier Saturday morning, the source said.

On Friday, the militants took control of the border crossing point with Syria which located just five kilometers west of al- Qaim, and also seized several border posts after clashes with the security forces, according to the source.

Dozens of militants attacked the base of the 28th Army Brigade on the edge of al-Qaim, as fierce clashes were underway with the troops, the source said, adding that Colonel Majid al-Fahdawi, the commander of the brigade, was killed during the tit-for-tat clashes with the militants to take control of the border area with Syria in the past two days.

Separately, a helicopter fired a rocket on a civilian car near the town of Saqlawiyah, just north of the militant-seized city of Fallujah, some 50 km west of Baghdad, killing five family members, including a man, two women and two children, a medical source from Fallujah hospital told Xinhua.

In eastern Diyala province, a joint force from soldiers, policemen and Shiite militiamen repelled an attack by Sunni militants on military bases in Imam Weis area, some 50 km northeast of the provincial capital city of Baquba, some 65 km northeast of Baghdad, Major General Jamil al-Shimary, provincial police chief, told Xinhua.

After several hours of battles, the security forces managed to kill 15 attackers and seized large amount of weapons and ammunition and a vehicle with heavy machine guns, al-Shimary said, adding that the troops have started a search operation in the area to hunt down the militants.

Diyala province, which stretches from eastern edges of Baghdad to the borders with Iran, has long been the stronghold of al-Qaida militant groups as well as a hotbed of insurgency and sectarian violence since the US-led invasion in 2003.

Iraq has seen a deteriorating security situation since June 10 when bloody clashes broke out between security forces and hundreds of Sunni militants who took control of Mosul and later seized swathes of territories after the Iraqi security forces withdrew from their posts in Nineveh and other predominantly Sunni provinces.