Trump blames Assad for chemical attack

US President Donald Trump has condemned a Syrian chemical weapons attack that killed dozens and blamed Syrian President Bashar al-Assad, but didn't say how he would respond despite calls from France for stronger US leadership.

Trump said the attack in Syria's Idlib province was "reprehensible and cannot be ignored by the civilised world", although he also sought to blame his predecessor, Barack Obama.

"These heinous actions by the Bashar al-Assad regime are a consequence of the last administration's weakness and irresolution," Trump said in a statement. "President Obama said in 2012 that he would establish a 'red line' against the use of chemical weapons and then did nothing."

The Syrian military denied responsibility and said it would never use chemical weapons.

The chemical weapons attack on Tuesday, which killed scores of people, including children, came a week after both Secretary of State Rex Tillerson and US Ambassador to the UN Nikki Haley said their focus in Syria was on stopping Islamic State militants rather than pushing Assad to leave power.

A senior Trump administration official said on Tuesday the government was looking at policy options after the attack in Idlib but that the options were limited and that the views expressed by Tillerson and Haley still held.