An advance group of chemical weapons inspectors have arrived in Syria to start overseeing the destruction of President Bashar Assad’s arsenal.

Twenty inspectors from a Netherlands-based watchdog crossed into Syria from neighbouring Lebanon on their way to Damascus to begin their complex mission of finding, dismantling and ultimately destroying an estimated 1,000-tons of chemicals.

They have about nine months to complete the task, which has been endorsed by a UN Security Council resolution that calls for Syria’s chemical stockpile to be eliminated by mid-2014. It is the shortest deadline that experts from the Organisation for the Prohibition of Chemical Weapons have ever faced in any nation, and their first mission in a country at war.

The team arrived in Damascus in a 19-vehicle convoy escorted from the border by two representatives from the Syrian Foreign Ministry.

Experts at The Hague, where the OPCW is based, said the priority is to achieve the first milestone of helping Syria scrap its ability to manufacture chemical weapons by a November 1 deadline, using every means possible. That may include smashing mixing equipment with sledgehammers, blowing up delivery missiles, driving tanks over empty shells or filling them with concrete, and running machines without lubricant so they seize up.

Some of the inspectors will be double-checking Syria’s initial disclosure of what weapons and chemical precursors it has and where they are located. Others will begin planning the logistics for visits to every location where chemicals or weapons are stored.

Within a week, a second group of inspectors is scheduled to arrive – fewer than 100 combined – and form teams that will fan out to individual sites. Their routes are secret – both for their safety and because Syria has the right not to reveal its military secrets, including base locations.

The inspectors’ mission was born out of the deadly chemical attack on opposition-held suburbs of Damascus on August 21 which prompted the Obama administration to threaten missile strikes against the Assad regime, touching off weeks of frantic diplomacy that ended with the UN resolution to purge Syria of its chemical weapons programme.