OSLO - It will be "difficult" to remove all of Syria's most toxic chemical weapons from the country by a December 31 deadline, Ahmet Uzumcu, the head of the global chemicals weapon watchdog OPCW said on Monday.But the head of the Organization for the Prohibition of Chemical Weapons, which has been charged with supervising the destruction of Syria's chemical arsenal, said a mid-2014 deadline to have all the weapons destroyed is realistic.Earlier on Monday, Syrian President Bashar Assad's forces have taken control of a highway connecting Damascus to the coast that is needed to extract hundreds of tons of toxic chemicals for destruction, a monitoring group said on Monday. Fighting in Syria poses a hurdle to implementing an agreement between Damascus and the Organization for the Prohibition of Chemical Weapons (OPCW) to remove the deadliest chemicals weapons by the end of the year to be destroyed.The army started an offensive in mid-November to secure the highway, which passes through the mountainous area of Qalamoun, roughly 50 km (30 miles) north of Damascus, stretches along the Lebanese border and hosts many military bases and outposts.The army has retaken the highway towns of Qara and Deir Attiyah from mostly Sunni Muslim rebels fighting to oust Assad, and has made inroads around the town of Nabak close to the road."The road is open but not safe," said Rami Abdulrahman, head of the anti-Assad Syrian Observatory for Human Rights monitoring group, adding that it remained vulnerable to rebel attack.Manar television, run by Lebanon's Shi'ite Hezbollah group and which has reporters embedded with the Syrian army, cited Syrian security sources as saying the highway was now secure. Rebels in the area did not respond to calls for comment. The government has never acknowledged that it did not fully control the road, a north-south artery that also links Damascus with the coastal stronghold of Assad's minority Alawite sect.Syria has agreed under a deal arranged by the United States and Russia to dismantle its chemical arsenal and destroy all its 1,300 tons of sarin, mustard gas and other lethal agents.The size of the stockpile, including 800 tons of industrial chemicals destined for incineration at commercial toxic waste plants, means it can only be transported by land and sea - using roads linking Damascus to the Mediterranean port of Latakia.The Hague-based OPCW, which won the Nobel Peace prize in October, has been charged with supervising the elimination of Syria's chemical arsenal. The US-Russian agreement averted planned US missile strikes after a sarin gas attack killed hundreds of people in the Damascus area in August.The United States is donating a naval ship and equipment to destroy Syria's chemical arsenal, but there is no agreement yet about where it will anchor while the work is carried out.Syria's conflict began with peaceful anti-Assad protests in March 2011 and developed into an armed insurrection when these were violently suppressed. More than 100,000 people have been killed and fighting has broadly settled into a bloody stalemate.