Britain is to give Syrian opposition fighters equipment to protect them against chemical weapons attacks "as a matter of special urgency", Foreign Secretary William Hague said on Tuesday.
The British government will supply "moderate" opposition fighters with 5,000 protective hoods, as well as pre-treatment tablets and chemical weapons detector paper to be used in a sarin gas attack.
Hague said the equipment costing some £657,000 ($991,0000, 757,000 euros) needed to be sent urgently as there was evidence that forces loyal to President Bashar al-Assad were using chemical weapons against the rebels.
"We believe that the use of chemical weapons is sanctioned and ordered by the Assad regime," he said in a written statement to parliament.
"We plan to equip the moderate armed opposition with 5,000 escape hoods, nerve-agent pre-treatment tablets (NAPs) and chemical weapons detector paper."
The United States and France have also accused the Assad regime of using banned arms including sarin, but Damascus has repeatedly denied the accusations.
The hoods protect wearers against the effects of sarin for up to 20 minutes, Hague said.
Someone wearing a hood would be able to move away from the area hit by the nerve agent, but they could not continue to fight.
The tablets, meanwhile, could give those hit by a sarin attack time to get to a medical centre to receive further treatment.
The equipment will be given to the Supreme Military Council of the Syrian National Coalition, which Britain recognises as the sole legitimate representatives of the Syrian people.
Hague has promised lawmakers that the government would seek parliament's consent before deciding to arm the rebels, amid concerns that they may fall into the hands of Islamist opposition groups.
Cameron said last month, however, that the government reserved the right to intervene in Syria if it felt Britain's national interests were under threat.
France said last month that it had provided the Syrian opposition with anti-sarin kits.
Originally developed as a pesticide, sarin was used by Iraqi dictator Saddam Hussein's regime to gas thousands of Kurds in the northern town of Halabja in 1988.
More than 100,000 people have been killed since the uprising against Assad erupted in March 2011, according to the Syrian Observatory for Human Rights.