Syrian state TV initially said on Monday the United States was suspected of carrying out a missile attack on the T-4 airfield near Homs, after harsh words by Trump over the reported chemical attack on Saturday in the town of Douma which killed dozens of people.

But the United States denied attacking the Syrian base, and France also said its forces had not carried it out.

The Russian military, whose forces are supporting Syrian President Bashar al-Assad, said two Israeli F-15 war planes had carried out the strikes on the Syrian T-4 air base, the Interfax news agency reported.

Interfax cited the Russian Defense Ministry as saying the Israeli war planes had carried out the strikes from Lebanese air space, and that Syrian air defense systems had shot down five of eight missiles fired.

Syrian state media, citing a military source, then carried a similar report. “The Israeli aggression on the T4 airport was carried out with F-15 planes that fired several missiles from above Lebanese land,” state news agency SANA said.

Israel had no immediate comment regarding the Syrian and Russian military charges.

Israel has struck Syrian army locations many times in the course of the conflict, hitting convoys and bases of Iranian-backed militias that fight alongside Assad’s forces.

Meanwhile, the United Nations Security Council will meet on Monday following rival requests by Russia and the United States after a deadly chemical attack in Syria and a warning by US President Donald Trump that there would be a “big price to pay.”

Russia called for a meeting of the 15-member council on “international threats to peace and security,” though the precise topic of discussion was not immediately clear, diplomats said on Sunday.

According to Reuters, a minute later the United States, France, Britain, Sweden, Poland, the Netherlands, Kuwait, Peru and Ivory Coast called for a meeting to discuss the chemical weapons attack in Syria, said diplomats who saw the email requests.

An agreement was reached late Sunday to hold one meeting on Monday instead of two, diplomats said.

“The Security Council has to come together and demand immediate access for first responders, support an independent investigation into what happened, and hold accountable those responsible for this atrocious act,” US Ambassador to the United Nations Nikki Haley said in a statement on Sunday.

Haley warned last month that if the UN Security Council fails to act on Syria, Washington “remains prepared to act if we must,” just as it did last year when it bombed a Syrian government air base over a deadly chemical weapons attack.

Trump said on Sunday there would be a “big price to pay” after medical aid groups reported dozens of people were killed by poison gas in a besieged rebel-held town in Syria. 

The Syrian government denied its forces had launched such an attack and Russia, President Bashar al-Assad’s most powerful ally, called the reports bogus.

A joint statement by the medical relief organization Syrian American Medical Society (SAMS) and the civil defense service, which operates in rebel-held areas, said 49 people had died in the attack late on Saturday in the town of Douma. US and other officials said they were working on Sunday to verify details of the attack, reported Reuters. 

Meanwhile the Organization for the Prohibition of Chemical Weapons (OPCW) announced on Monday it was investigating allegations of the chemical weapons attack in Syria on Saturday. 

In a statement on their website, OPCW Director-General Ambassador Ahmet Üzümcü, expressed his grave concern over claims and said: “The OPCW Situation Centre has been closely monitoring the incident and made a preliminary analysis of the reports of the alleged use of chemical weapons immediately after they were issued. 

“The Fact Finding Mission (FFM) is in the process of gathering further information from all available sources to establish whether chemical weapons were used. The FFM will report its findings to States Parties to the Chemical Weapons Convention,” Üzümcü said.  

The Chemical Weapons Convention comprehensively prohibits the use, development, production, stockpiling and transfer of chemical weapons. 

In response to persistent allegations of chemical weapon attacks in Syria, the FFM was set up in 2014 “to establish facts surrounding allegations of the use of toxic chemicals, reportedly chlorine, for hostile purposes in the Syrian Arab Republic”.  

Since May 2014, the OPCW has deployed the FFM on numerous occasions to Syria. 

The FFM in the past established the facts surrounding allegations of the use of toxic chemicals as weapons in Syria and confirmed that chemical weapons had been used in the past. 

This move came just hours after said on Twitter that Syrian President Bashar al-Assad will have a “big price to pay” for launching the chemical weapons attack on civilians, and blamed Iran and Russian President Vladimir Putin for backing “animal Assad.”

“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,” Trump wrote on Twitter.

“President Putin, Russia and Iran are responsible for backing Animal Assad. Big price to pay,” he wrote.