The Latest on Syria (all times local):

1:05 p.m.

A British delegation at a behind-closed-doors meeting of the international chemical weapons watchdog says in a tweet that the organization's director general has said that its investigators already are testing samples from a suspected deadly chemical weapons attack in Syria's Idlib province.

The British delegation tweet says that Organization for the Prohibition of Chemical Weapons Director-General Ahmet Uzumcu told Thursday's hastily convened meeting of its executive council that the "Fact Finding Mission is working to gather evidence" about the April 4 attack in Khan Sheikhoun that killed nearly 90 people.

It says that samples already are being tested and the mission is expected to report its findings in three weeks.

The OPCW's Fact Finding Mission in Syria investigates alleged attacks, but does not apportion blame.

12:50 p.m.


U.S.-backed Syrian Kurdish forces say they have entered the fourth stage of their campaign to capture the Islamic State group's de facto capital Raqqa with an advance on the militants in a valley north of the city.

The Syrian Democratic Forces, which include Arab fighters, say they are working to clear the militants out of the Jalab Valley, north of Raqqa. An estimated 300,000 people are in the city.

The SDF says it wants to isolate Raqqa before attacking it. Their closest position is within 8 kilometers (5 miles) northeast of the city. But the countryside south of Raqqa is still under IS control.

It is unclear how many stages are planned for the SDF campaign.