The White House on Saturday condemned the Assad regime's "defiance" of international norms after United Nations experts found the Syrian army had conducted three chemical weapons attacks against its own people in 2014 and 2015.

Of the nine alleged chemical attacks it is considering in its ongoing probe, the U.N.-led joint investigative mechanism has now attributed three to the Syrian government and one to the Islamic State group.

Iraqi forces battled Sunday through booby-traps, sniper fire and suicide car bombs to tighten the noose around Mosul, while also hunting Islamic State group jihadists behind attacks elsewhere in the country.

The pro-government Arab coalition Sunday stepped up air strikes on Iran-backed rebels in Yemen and clashes raged on the ground as warring parties ignored a U.N. call to renew a fragile ceasefire.

Heavy clashes erupted between regime and rebel forces in Syria's divided city of Aleppo after a "humanitarian" ceasefire announced by government ally Russia expired before the U.N. could evacuate wounded civilians from rebel-held areas.

The Aleppo that Ibrahim al-Haj's son Laith was born into 10 months ago is now being destroyed.

The opposition-held districts of the Syrian city have been surrounded and under siege for months. Russian and Syrian warplanes are bombing the streets into rubble and government forces are chipping away at the pocket of opposition control. For the 270,000 people holding out there, everything is getting harder to find — food, drinkable water and fuel. Residents are planting vegetables in bomb craters and digging wells.

The entire territory of Syria must be "liberated," Russian President Vladimir Putin's spokesman said in remarks televised Saturday, dismissing demands for Syrian President Bashar Assad's departure as "thoughtless."

Dmitry Peskov said Assad needs to stay in power to prevent the country from falling into the hands of jihadis.

An Iraqi cameraman was killed on Saturday covering a military offensive to wrest the city of Mosul back from the Islamic State group, his channel said.

The young reporter was killed "covering the battle" near the village of Al-Shura, south of Mosul, Al Sumaria TV said in a short news flash on its website.

A senior Egyptian army officer was shot dead outside his home in a Cairo suburb on Saturday, a military official and a relative told AFP.

Jihadists have killed hundreds of policemen and soldiers, mostly in the Sinai Peninsula, but such attacks on senior officers are rare.

Turkey hit Syrian Kurdish militia targets in northern Syria for the second time in less than 72 hours, the military said Saturday, quoted in state media.

Rockets struck 70 People's Protection Units (YPG) targets Friday, the armed forces said in a statement, but did not say if any militia fighters were killed.

Hundreds of wounded civilians were stranded in rebel-held areas of Syria's Aleppo Saturday after the UN said security concerns had prevented evacuation convoys even as Russia extended a ceasefire into a third day.

The unilateral "humanitarian pause" in the Syrian army's devastating Russian-backed assault on the opposition-controlled east of the city has largely held since it began on Thursday morning.