The United Nations said Sunday its experts would start their probe of an alleged Syrian chemical weapons site Monday.
Secretary General Ban Ki-moon "has instructed the mission ... currently in Damascus, to focus its attention on ascertaining the facts of the 21 August incident as its highest priority," the UN said in a statement.
"The mission is preparing to conduct on-site fact-finding activities, starting tomorrow, Monday, 26 August."
The mission had been repeatedly delayed amid differences with President Bashar al-Assad's regime over the scope of the probe into the alleged use of chemical arms in the 29-month civil war.
The UN announcement came shortly after Damascus gave the green light for the inspectors to carry out the probe into the alleged use of chemical weapons near the Syrian capital on Wednesday.
Doctors Without Borders has said 355 people died last week of "neurotoxic" symptoms, after the opposition claimed regime forces unleashed chemicals east and southwest of Damascus causing more than 1,300 deaths.
Ban "notes the Government of the Syrian Arab Republic affirmed that it will provide the necessary cooperation, including the observance of the cessation of hostilities at the locations related to the incident," the UN statement said.
"The Secretary-General would like to reiterate that all relevant parties equally share the responsibility of cooperating in urgently generating a safe environment for the mission to do its job efficiently and providing all necessary information."
The UN team arrived in Damascus last week to begin the hard-won mission, which UN officials originally said would last two weeks and cover three sites.