Secretary-General Ban Ki-moon?on Thursday?reiterated his grave concern about Syria's chemical weapons and recent reports of plans for their possible use, and has written again to President Bashar al-Assad urging him to refrain from the use of any such weapons, according to his spokesperson.

Ban discussed the issue in a telephone call with Ahmet üzümcü, the Director-General of the Organisation for the Prohibition of Chemical Weapons (OPCW), which oversees the convention aiming to eliminate the use, development, production and transfer of these deadly weapons.

Violence has gripped Syria since protests that began against?al-Assad 21 months ago turned into a revolt amid a crackdown by authorities. Civilians make up the vast majority of the at least 20,000 people killed in the conflict, while 2.5 million Syrians need humanitarian assistance, and another 475,000 have fled the country and have either registered, or are registering, as refugees, according to UN estimates.

According to information provided by Ban's spokesperson, the Secretary-General had conveyed his concerns in writing already some months ago to?al-Assad and he did so again in a letter handed over to the Syrian authorities on Tuesday, in which he urged the Syrian leader to refrain from the use of any such weapons under any circumstances.

The UN chief also underscored the fundamental responsibility of the Syrian Government to ensure the safety and security of any such stockpiles, and reiterated to üzümcü that any use of such weapons would be an outrageous crime with dire consequences, the spokesperson added.

Syria is one of eight States that have not yet joined the Chemical Weapons Convention which currently has 188 States Parties. The others are Angola, the Democratic People's Republic of Korea, Egypt, Israel, Myanmar, Somalia and South Sudan.