PARIS (AFP) - US President Donald Trump and his French counterpart Emmanuel Macron agreed during a telephone call on Tuesday (June 27) on the need for a "joint response" in the event of another chemical attack in Syria, the French presidency said.

Their call came a day after Washington said that Syrian President Bashar al-Assad may be preparing another chemical weapons attack and warned that his regime would pay a "heavy price" if it went ahead with such an assault.

A Pentagon spokesman said US intelligence had noticed suspect activity at the launch site of the regime's apparent chemical strike in April.

Days after that strike on a rebel-held town, the United States launched a cruise missile strike on the airfield in retaliation - the first direct US attack on the Syrian regime.

The French foreign ministry refused to say Tuesday whether it too had information about possible preparations by the Syrian regime for a chemical attack.

After a meeting last month with Russian President Vladimir Putin, an Assad ally, Macron drew a "very clear red line" on the use of chemical weapons "by whomever" and warned of reprisals.

In August 2013, a chemical attack near Damascus brought France and the US to the brink of a joint military intervention in Syria.

But then US president Barack Obama, who had also declared that a chemical attack would cross a "red line", eventually decided against military action.

The US and Russia instead struck a deal on the destruction of Syria's nuclear weapons stockpile.