A picture taken on April 8, 2018, shows smoke billowing as Syrian Army soldiers advance in agricultural land on the eastern outskirts of Douma, as they continue their fierce offensive to retake the last opposition holdout in Eastern Ghouta. (AFP photo)

The Syrian army said Israeli F-15 warplanes had carried out the attack on the T-4 air base in central Syria before daybreak Monday by firing missiles from the Lebanese airspace, according to the state TV.

The Israeli warplanes fired several rockets from inside the Lebanese airspace and targeted the T-4 air base in the eastern countryside of the Homs province in central Syria.

The Syrian air defenses responded to the attack, destroying several rockets before reaching their destination.

The attack was carried out before daybreak Monday and was initially thought to be carried out by the United States, which has recently threatened retaliation against the Syrian army over allegations made by the rebels about the use of chlorine gas in a recent attack on the Douma district, the last rebel-held area in Eastern Ghouta.

Earlier in the day, the Syrian Observatory for Human Rights said a total of 14 people, including troops of Iranian forces allied to the government, were killed in the missile strike.

State media outlets said several loud explosions were heard early on Monday near the airfield in the eastern countryside of Homs. It was later confirmed to be a missile attack targeting the military facility.

US Pentagon spokesman Christopher Sherwood denied the report in a statement, saying the US Department of Defense "is not conducting airstrikes in Syria at this time."

The attack came amid an international wrangling about the allegations of the use of chemical weapons by the Syrian army in the attack on the rebels in Douma district.

The pro-rebel Ghouta Media Center has claimed that nerve agent sarin and chlorine gas have been used in Syrian army's recent offensive in Douma, which has caused civilians to suffocate and choke.

The Syrian government has strongly denied its possession of chemical weapons, saying such allegations were fabricated to deliberately frame the government forces.

Western countries, such as the United States and Britain, have warned that they would respond with military action if the Syrian army is proven to have used chemical weapons in its attacks.

US President Donald Trump on Sunday promised that a "big price" would be paid for what he called a chemical weapons attack on Douma on Saturday.

Thomas Bossert, Trump's homeland security adviser, said the president's national security team had been in talks with Trump late Saturday and early Sunday about how to respond to the alleged chemical attack in Douma.

Douma is the last rebel-held area in Eastern Ghouta. Earlier, the rebels of the Islam Army in the area backed down on an agreement they had concluded with the Syrian government and Russia on their evacuation from Douma and refused to release kidnapped people from its prisons.

But on Sunday, the Islam Army agreed to evacuate after a weeks-long military operation by government forces and released the first batch of kidnapped people from its prisons.

Also, buses transporting Islam Army rebels and their families have gathered at the assembly point in the Wafideen area northeast of Damascus to prepare to leave for the rebel-held city of Jarablus in northern Syria.

Monday's missile strike is not the first foreign attack against Syria, as the United States targeted the Shayrat air base in the countryside of Homs in April last year to punish alleged use of chemical weapons by the Syrian army on a rebel-held area in the northwestern province of Idlib.

Israel has also carried out several attacks on Syria air bases on the pretext of targeting positions of the Iranians and the Shiite Hezbollah group.