Turkey: Russia backs independent probe into use of chemical weapons in Syria
Russia has agreed to support an independent investigation into the use of chemical weapons in northern Syria, Turkish President Recep Tayyip Erdogan has said.
Mr Erdogan's office said he and Russian President Vladimir Putin had agreed to back a probe by the Organisation for the Prohibition of Chemical Weapons (OPCW).
A spokesman said the two leaders held a telephone conversation on Thursday, during which the Turkish leader stressed that the use of chemical weapons "is the greatest crime against humanity".
A statement said: "The two leaders agreed that the attack in question be investigated by the OPCW, which is an independent organisation whose legitimacy is recognised."
Mr Erdogan and Mr Putin also discussed peace efforts for Syria and their joint efforts to extend a ceasefire agreement to the whole of the country.
Meanwhile, a misdirected airstrike by the US-led coalition earlier this week killed 18 allied fighters battling the Islamic State group in Syria, the US military said.
US Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the predominantly-Kurdish Syrian Democratic Forces, for a strike intended to target IS militants south of their Tabqa stronghold, near the extremists' de facto capital, Raqqa.
The strike hit an SDF position instead, killing 18.
Central Command said the strike was launched on Tuesday.
Several nations have lent their air power to the US-led coalition to defeat the Islamic State group. It was not clear which air force was behind the strike.
The SDF acknowledged the strike on Thursday, saying a number of its fighters were killed and wounded.
The SDF-linked Hawar News Agency reported the group was holding funerals for 17 of its fighters in the border town of Tal al-Abyad, though it did not link them to the strike.
An activist-run group, Raqqa is Being Slaughtered Silently, says three days of mourning have been declared for the town.
The Britain-based Syrian Observatory for Human Rights said 25 SDF fighters were killed in the last two days of battle.
The SDF meanwhile announced the launch of a fourth phase of their campaign to capture Raqqa, a Euphrates River city that is home to 300,000 people.
The SDF, with US-led air and ground support, has surrounded Tabqa, some 25 miles south west of Raqqa. They say they are working to clear Islamic State militants out of Jalab Valley, north of Raqqa.
The SDF says it wants to isolate Raqqa before attacking it. Their closest position is less than five miles north east of the city.
But the countryside south of Raqqa is still under IS control. It is unclear how many stages are planned for the campaign.
In a separate development, President Bashar Assad said a chemical attack on a rebel-held town earlier this month that was widely blamed on his forces was a "fabrication".
"Definitely, 100% for us, it's fabrication", Mr Assad told Agence France-Presse in his first comments since a US missile strike on a Syrian air base in response to the chemical attack.
"Our impression is that the West, mainly the United States, is hand-in-glove with the terrorists. They fabricated the whole story in order to have a pretext for the attack."
Syria strongly denied it was behind the April 4 chemical attack on Khan Sheikhoun, which killed 87 people.