Syria is on target to meet a looming deadline to destroy its chemical weapons production equipment, even though inspectors have yet to visit all sites, UN leader Ban Ki-moon said Monday.

"The functional destruction of the declared capacity of the Syrian Arab Republic is expected to be completed as planned by November 1," Ban said in a report to the UN Security Council obtained by AFP.

Inspectors from the Organization for the Prohibition of Chemical Weapons (OPCW) and UN have however only been to 21 of the 23 sites declared by President Bashar al-Assad's government because of the country's conflict.

Destruction of the chemical production and mixing facilities is the first major deadline of a tight timetable set out by the Security Council to eliminate all of Syria's chemical weapons by June 30 next year.

Syria still has an estimated 1,000 tonnes of chemicals to be destroyed and no plan has yet been agreed for the risky operation, officials said.

The inspectors have "confirmed the functional destruction of the production and mixing and filling capabilities at all the sites" inspected so far, Ban said.

The UN leader stressed that the deadline should be met "a mere" 34 days after the 15-nation Security Council ordered the destruction of all of Syria's chemical weapons.

"In all of these activities the government of the Syrian Arab Republic has extended consistent, constructive cooperation," Ban said.

There are 22 OPCW experts and about 50 UN staff supervising the destruction program so far, the UN report said.

Syria has declared 41 facilities at the 23 sites and so far only 37 have been inspected, Ban added. He said they would go to the last sites "as soon as condiions permit." The report did not say if the unsafe sites were in government or opposition territory.

The UN report said security "remains difficult and unpredictable" for the inspectors because of the 31 month old war which the UN says has left well over 100,000 dead.

And the UN leader highlighted the major security and logistics task ahead to get rid of Syria's chemicals in line with the Security Council deadline.

Syria has submitted an "initial plan" for the transportation of chemicals for destruction, the report said without giving details.

"The job is far from complete and much important work remains to be done," Ban said.

"Without sustained genuine commitment by the Syrian authorities, the joint mission will not fullfil its objectives," he warned.

The Security Council passed a resolution ordering the destruction of Syria's chemical arms amid tensions over a threatened US military strike on the facilities.

The United States and other western countries have blamed the Assad government for an August 21 chemical weapon attack near Damascus in which hundreds died.

The government has blamed Syrian rebels.

A UN inquiry determined that sarin gas was used in the assault. It is due to report this week on whether chemical weapons were used in other Syrian towns.