The deal was reached after two UN envoys went to Syria on Tuesday and Wednesday and held talks with Syria's deputy prime minister and foreign minister.

"The discussions were thorough and productive and led to an agreement on the way forward," said the statement on Friday.

Ake Sellstrom, the chief inspector in the UN investigation team, and Angela Kane, the UN high representative for disarmament, are expected to report to UN chief Ban Ki-moon about the agreement.

The envoys arrived in the Syria capital Damascus at the invitation of the Syrian government to secure a deal for starting investigation into allegations of chemical weapons use in the Arab country.

The Syrian government has already filed several reports containing evidence that the militants used chemical weapons in their attacks on civilians and Syrian army soldiers. Militants, in return, accuse the army of doing so.

A Russian-led inquiry has already revealed that militants carried out a chemical attack in the village of Khan al-Assal on the edge of the northern city of Aleppo in March, which killed 26 people.

On May 6, UN investigator, Carla Del Ponte, said testimony from victims of the conflict in Syria suggests militants have used the nerve agent, sarin.

Sarin is a colorless and highly toxic nerve agent that can cause convulsions, paralysis and death within minutes if it is absorbed through inhalation, ingestion, or contact with skin or eyes.

Sarin is classed as a weapon of mass destruction and is banned under international law.

SHI/SHI