By Dominic Evans
BEIRUT (Reuters) - Syrian army and militia troops loyal to President Bashar al-Assad have pushed back a rebel offensive in the mountain heartlands of his Alawite sect, officials and activists said on Monday, after days of heavy fighting and aerial bombardment.
The assault by Islamist rebels on the northern edges of the Alawite mountains overlooking the Mediterranean drove hundreds of Alawite villagers out to the coast and marked a major challenge to Assad's reassertion of power over central Syria.
But the Syrian president, battling a two-year uprising which has descended into a devastating civil war, sent reinforcements to the rugged area of northern Latakia to repel the attack.
The Syrian Observatory for Human Rights monitoring group said Assad's forces have retaken all the military observation posts which rebels had seized when they launched their offensive two weeks ago, and regained control of nine Alawite villages.
The army was still trying to recapture two villages, the observatory's head Rami Abdelrahman said, adding that heavy fighting continued on Monday.
State news agency SANA said the army had "dealt with the last terrorist groups" in the area and seized their weapons.
Rebels killed 200 people, mostly civilians, and drove hundreds from their villages in the first three days of the assault, activists said. They also shot down a military jet, according to amateur video footage released on Sunday.
At one stage a rebel commander said the rebels had reached within 20 km (12 miles) of Qardaha - Assad's hometown and the burial place of his father Hafez al-Assad, who ruled Syria with an iron fist for three decades.
In a gesture of support for the rebel fighters, and a sign of the symbolic significance of their advances, the head of the Free Syrian Army was filmed visiting Latakia province last week.
But the army and pro-Assad National Defence Force militia fighters pushed the rebels back, killing many fighters including foreign Arab jihadists who formed part of the al Qaeda-linked brigades on the rebel front line.
Jets have also bombed the Sunni Muslim town of Salma which was the launchpad for the rebel attack against the Alawite villagers, a minority sect that is an offshoot of Shi'ite Islam.
Syria's conflict, which has killed more than 100,000 people, began as peaceful protests demanding Assad's ouster but is now marred by rising sectarian bloodshed between Sunnis and Alawites.
A team of United Nations chemical weapons experts arrived in Damascus on Sunday after months of delay and were due to start investigating reports dating back to last December about the possible use of chemical weapons in Syria's civil war.
The government and rebels accuse each other of using chemical weapons, a step which the United States has said would cross a "red line" in the conflict.
Like the broader Syrian war, the issue of chemical weapons has divided world powers. The United States said in June it believed Assad's forces have used them on a small scale, while in July Russia said rebels fired sarin gas near Aleppo in March.
The U.N. team, including weapons experts from the Organisation for the Prohibition of Chemical Weapons, will try to establish only whether chemical weapons including sarin and other toxic nerve agents were used, not who used them.
"This is the first probe of allegations of the use of weapons of mass destruction in the 21st century," U.N. Secretary-General Ban Ki-moon said on Monday.
"If confirmed, the use of chemical weapons by any side under any circumstances must be held accountable and would constitute an international crime," he told a news conference.
The team was due to visit three sites in Syria, including Khan al-Assal in the north, but it was not immediately clear when they would make those trips.
"In order to credibly establish the facts, the mission must have full access to the sites of the alleged incidents," Ban said.
"This includes access to the reported sites to undertake the necessary analyses and to collect samples. It also includes interviews and examination of witnesses, victims, attending medical personnel as well as the conduct of post mortem examinations," he added.
Syria's turmoil has not only torn the country apart, it is also dragging in neighboring countries and stoking regional sectarian tensions. Foreign Sunni fighters have flocked to Syria to battle Assad, and Lebanese and Iraqi Shi'ites have joined the fight on the president's side.
Fighters from al Qaeda's Islamic State in Iraq and the Levant have also increasingly clashed with Kurds in the north and northeast of the country - one factor behind a recent wave of refugees into Kurdish northern Iraq.
More than 20,000 people have entered northern Iraq since Thursday in one of the largest crossings since the conflict erupted in March 2011, some coming from as far away as Aleppo, 450 km (280 miles) to the west.
The border between Syria and Iraq has been largely closed since authorities of the Kurdish regional government shut the crossing on May 19, apart from a single formal crossing point at Al-Wahid in Anbar province.
The latest influx of refugees crossed a new pontoon bridge over the Tigris river at Peshkhabour, adding to the 150,000 Syrian refugees already registered in Iraq.
The total number of refugees who have fled Syria is now close to 2 million, and has nearly doubled in just five months, leading some of Syria's neighbors to tighten border controls to stem the flows in recent weeks.
(Additional reporting by Michelle Nichols at the United Nations; Editing by Raissa Kasolowsky and Will Dunham)