The monthly report to the UN Security Council of the joint mission of the United Nations and the Organization for the Prohibition of Chemical Weapons said on Wednesday that the attempted attacks were on January 27. It gave no details on the location of the convoys.

"In addition, Syrian authorities indicated that ongoing military activities rendered two sites inaccessible during most of the reporting period," the five-page report said.

This delayed "in-country destruction of the final quantities of isopropanol, preventing some activities to consolidate chemical material into a reduced number of locations, and preventing the physical verification of chemical material prior to movement on 27 January 2014."

Isopropanol is one of two key ingredients for sarin.

President Bashar al-Assad agreed to destroy Syrian chemical weapons following global outrage over an alleged sarin gas attack in August.

It sparked a US threat of military strikes that was averted after the Syrian government pledged to give up his chemical arms.

But the Syrian government, locked in a three-year-old war with rebels seeking to overthrow Assad, failed to meet the February 5 OPCW deadline to move all of its declared chemical substances and precursors - some 1,300 tonnes - out of the country.

Syria has now proposed a new timetable to remove its chemical weapons by late April, diplomats said on Wednesday.

BA/BA