More than 2,000 Iraqi troops were rushed to seal the porous desert border near Qaim, the Syrian side of which has been controlled by rebels for two days, an Iraqi general said.

He said there appeared to be no Syrian forces between the border at Qaim and the nearest Syrian city, Deir ez-Zour, about 130 kilometres (80 miles) away. The area is traditionally controlled by Sunni tribes.

At Qaim itself, the army sealed off the border crossing with waist-high concrete blast walls.

Clusters of Iraqi soldiers could be seen at the border crossing on Friday, and plumes of black smoke billowing from the Syrian side.

Iraq's government spokesman said Syrian rebels are controlling one major border crossing between the two counties, but three others remain in the hands of the Syrian regime and continue to process the fleeing migrants.

Iraq's government spokesman indicated Friday that the country would not open its borders to Syrian refugees trying to flee fighting across from al-Anbar province.

Ali al-Dabbagh told state-run Iraqiya TV that Iraq's fragile security and the borders' remote location prevented them from supporting refugees.

"We are sorry for not receiving Syrian refugees. We are not like Jordan and Turkey -- their border regions can provide services. We had hoped to help our Syrian refugee brothers."

Iraq sealed al-Qaim - one of two border crossings with Syria in its Western al-Anbar province after opposition fighters captured the Syrian side of the crossing, Alboukamal. The Iraqi government has moved an army division to reinforce the border between al-Qaim and the main entry point of Waleed and sealed the entry gate to Syria with concrete blast barriers.

The UNHCR says it has appealed to Iraq to reopen the border to refugees.