US, France set Syria redline

US President Donald Trump and his French counterpart Emmanuel Macron agreed Tuesday on a joint response in the event of another chemical attack in Syria, as Washington warned Damascus would pay a "heavy price" for such a move.

The tough language, in a phone call between the two leaders, came a day after the White House accused President Bashar al-Assad's regime of preparing a potential chemical weapons attack.

Washington's warning to Damascus -- which prompted criticism from regime allies Russia and Iran -- coincided with a wave of US-led coalition air strikes that killed nearly 60 people at a Syrian prison run by the Islamic State group.

The coalition has been striking IS in Syria and Iraq since mid-2014 but has also been involved in recent confrontations with Assad's forces, raising fears of the United States being drawn into Syria's civil war.

A Pentagon spokesman said Tuesday that US intelligence had noticed suspect activity at the launch site of an apparent chemical strike by the regime two months ago.

The April attack on the rebel-held town of Khan Sheikhun was reported to have killed at least 87 people, including many children, and images of the dead and of suffering victims provoked global outrage.

Washington launched a retaliatory cruise missile strike days later against the Shayrat airbase where it said the attack was launched -- the first direct US action against the regime, which denies any use of chemical weapons.

White House spokesman Sean Spicer warned Monday night that if "Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price."

After a meeting last month with Assad's ally, Russian President Vladimir Putin, Macron had drawn a "very clear red line" on the use of chemical weapons in Syria and warned of reprisals.

America's warning to Damascus drew condemnation both from the Kremlin, which said it considered "such threats against the Syrian leadership to be unacceptable," and from Tehran.

"Another dangerous US escalation in Syria on fake pretext will only serve ISIS, precisely when it's being wiped out by Iraqi and Syrian people," Foreign Minister Mohammad Javad Zarif tweeted.

Monday's coalition strikes hit an IS-run jail in Syria's Mayadeen at dawn, according to the Syrian Observatory for Human Rights, a Britain-based war monitor which said they killed 42 prisoners and 15 jihadists in Mayadeen, a large town in the eastern province of Deir Ezzor.

Pentagon spokesman Adrian Rankine-Galloway confirmed coalition strikes on Mayadeen on Sunday and Monday, targeting IS "command and control facilities" and other "infrastructure".

A monitoring group yesterday said that at least 30 civilians were killed in air strikes on an area of eastern Syria held by the Islamic State group. The Syrian Observatory for Human Rights said it was not immediately able to say whether the strikes in Deir Ezzor province yesterday were carried out by the US-led coalition, or by the Syrian army or its Russian ally.

In another development, the Turkish army and Syrian Kurdish militia have exchanged fire in northern Syria, the Turkish military said yesterday, amid growing tensions in the border region.