The UK has said it will destroy a further 50 tonnes of material from Syria's chemical weapons stockpile.

The move on Wednesday would take the total amount the country has agreed to process to 200 tonnes.

Facing the threat of US air strikes, Bashar al-Assad's government last year promised to dismantle its chemical arsenal, telling the Organisation for the Prohibition of Chemical Weapons (OPCW) it had 1,300 tonnes of such weapons.

Britain had previously agreed to accept 150 tonnes of Syrian poison gas precursors for destruction by French firm Veolia Environnement in northern England. 

"A further 50 tonnes of the industrial chemicals hydrogen chloride and hydrogen fluoride will also be destroyed in specialised commercial facilities in the UK," Foreign Secretary William Hague said in a written statement to parliament.

Hague said a ship carrying the chemicals was expected to arrive in Britain next week.

Foreign powers have scrambled to find countries to destroy the chemicals. The most toxic are first being processed on board a US ship.

Less dangerous precursor chemicals are being destroyed commercially at industrial facilities.

Source: Agencies