Syrian air defences shot down eight missiles after a major air base in central Syria was struck, Syrian state television reported.
The state broadcaster said explosions were heard at the T-4 airfield near Homs, which is close to the ancient city of Palmyra in central Syria. It said there were several dead and wounded.
Syrian state media said they were suspected to be US strikes but US officials said that the US military had not launched air strikes.
Pentagon spokesman Christopher Sherwood said: "At this time, the Department of Defence is not conducting air strikes in Syria."
A suspected poison gas attack on Sunday on the besieged town of Douma that killed 70 people, including children, came almost exactly a year after a US missile attack prompted by deaths in Khan Sheikhoun. The US launched several dozen Tomahawk cruise missiles at a Syrian air base after a chemical attack in the northern Syrian town killed dozens of people. Israel has also struck inside Syria in recent years.
In response to the reports from Douma, US President Donald Trump yesterday blamed Syrian government forces for what he called a "mindless CHEMICAL attack." In a series of tweets, Trump held Russia and Iran, Syrian President Bashar Assad's chief sponsors, responsible.
In a phone call with Trump, French President Emmanuel Macron strongly condemned the "chemical attacks," and the pair vowed a "strong, joint response," the White House said.
The Syrian Government denied the allegations, calling them fabrications.
Trump warned Russia's Vladimir Putin that there would be a "big price to pay" for the suspected Syrian chemical weapons attack. In his harshest criticism of the Russian leader since taking office, the US President said Putin was partly "responsible" for the assault on rebels in Douma, Eastern Ghouta.
He also criticised former President Barack Obama's failure to police a "red line" over chemical weapons, while a senior White House official said no form of response was "off the table".
The comments raise the possibility of a US air strike against Bashar al-Assad, the Syrian President. The UN security council is expected to meet today after the UK, France, the US and six other countries called for an emergency session.
Russia, Iran and Syria all denied chemical weapons had been used, with the Kremlin warning that any military response from the West would be "absolutely unacceptable".
A residential area of Douma, one of the last remaining rebel-held pockets in Syria, was struck. Footage showed the dead bodies of children and adults with foaming mouths and glaring eyes.
Trump tweeted: "Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price to pay.
"Open area immediately for medical help and verification. Another humanitarian disaster for no reason whatsoever. SICK!"
- Telegraph Group Ltd, AP