BEIRUT • A dense sandstorm engulfing parts of the Middle East left at least 12 people dead and hundreds suffering from respiratory problems as officials warned residents to stay indoors.

Large parts of Lebanon, Syria, Israel and Cyprus were shrouded in a thick cloud of dust from the storm that began sweeping into the region on Monday.

Refugees from Syria now living in basic conditions in Lebanon were badly affected.

In Syria, Al-Qaeda's affiliate and its allies seized the last regime-held military base in north-western Idlib province yesterday amid the sandstorm, in the latest setback for President Bashar al-Assad's forces.

Al-Nusra Front and a coalition of mostly militant groups captured the Abu Duhur military airport after a siege that lasted two years, the Syrian Observatory for Human Rights monitor said.

Observatory chief Rami Abdel Rahman said the forces appeared to have taken advantage of the massive sandstorm that made it difficult for the regime's aircraft to carry out strikes.

The sandstorm also led to the deaths of at least six people across Syria from respiratory failure, the monitor said.

Lebanon's Health Ministry said at least two women had died at hospitals in the eastern Bekaa Valley region because of the storm, without specifying their nationality.

"The number of cases of choking and shortness of breath caused by the sandstorm has risen to 750," the ministry said.

Police distributed face masks on city streets as the authorities warned people suffering from health problems, the elderly and pregnant women to stay indoors.

The storm was felt particularly in Lebanon's dozens of informal camps where hundreds of thousands of Syrian refugees live with limited shelter.

Mr Mouin Hamzeh, secretary-general of Lebanon's governmental National Council for Scientific Research, said satellite images "clearly show that the sandstorm came from northern Iraq in the direction of central and northern Lebanon, north and east Syria, and southern Turkey".

"It usually happens twice or even three times a year in Lebanon but during spring, March and April, and the unusual thing today is the density of the storm," he said.

AGENCE FRANCE-PRESSE