♦ Syria denies having chemical weapons after France's strike threat
♦ Turkey demands US expel Kurdish militia from anti-IS force as rift widens
The UN special envoy for Syria has given warning that violence in the country is the worst he has seen since taking the job four years ago.
Staffan de Mistura's remarks on Wednesday came as the US and Russia again traded blame at the UN over the ongoing conflict.
Next month the war in Syria will enter its eighth year with diplomatic efforts stalled as violence rages on the ground.
"Civilians have been killed on a horrific scale - reports suggest more than 1,000 civilians in the first week of February alone," he told the UN Security Council.
"I have been now four years as the special envoy. This is as violent and worrying and dangerous a moment as any that I have seen in my time of tenure so far."
De Mistura mentioned all the countries now fighting in Syria, including the Turkish operation around Afrin and the Syrian government's continued bombardment of Eastern Ghouta and Idlib.
He talked of developments in recent days, including the US attack on Assad's forces near Deir Az Zor and Israeli air attacks in Syria including on Iranian targets. But both these operations were later defended by Nikki Haley, the US ambassador to the UN.
She criticised Russia for failing to stop the Assad regime from bombing and gassing civilians, drawing a sharp response from Moscow's permanent representative to the UN, Vassily Nebenzia.
Nebenzia said the US and its allies should use their influence over the opposition groups to prevent violence.
Meanwhile, the Syrian government on Wednesday denied it possessed chemical weapons and branded the use of such arms "immoral and unacceptable", following a French warning of punitive strikes.
France's President Emmanuel Macron warned on Tuesday that his country would launch strikes if proof emerged that the Syrian regime had used banned chemical weapons against its civilians.
This was reaffirmed on Wednesday by his foreign minister, Jean-Yves Le Drian, who spoke of "military strikes" in case of any new chemical attacks "since these attacks are lethal and the responsibility of the regime is proven".
According to Washington, at least six chlorine attacks have been reported since early January in rebel-held areas, resulting in dozens of injuries.
Meanwhile, Turkey yesterday said it had demanded that the United States expel a Kurdish militia from the ground forces it backs in Syria, underscoring the widening gulf between the Nato allies since Ankara launched a new Syrian offensive last month.
Ties between Turkey and the United States, both allies in a US-led coalition fighting against Islamic State, have been strained to the breaking point by Washington's support for the Syrian Kurdish YPG militia, which Ankara sees as terrorists.
Ankara considers the YPG to be an arm of the PKK, a banned group that has waged a decades-long insurgency in Turkey.
"We demanded this relationship be ended, I mean we want them to end all the support given to the Syrian arm of PKK, the YPG," Turkish Defence Minister Nurettin Canikli told reporters in a briefing in Brussels, a day after meeting US Defense Secretary Jim Mattis on the sidelines of a Nato meeting.
Speaking with reporters on the sidelines of the Nato meeting, Mattis said his talks with his Turkish counterpart were open and honest, but acknowledged the differences.
A U.S. statement said Mattis had urged Turkey to keep attention on fighting Islamic State: "He called for a renewed focus on the campaign to defeat IS, and to preventing any vestige of the terrorist organization from reconstituting in Syria," it said, using an acronym for Islamic State.