A total of 14 people, including troops of Iranian forces allied to the government, were killed in a missile strike that targeted an airbase in central Syria before daybreak Monday, a monitor group reported.
The Syrian state TV had earlier reported that the T-4 airbase in the Syrian central province of Homs was hit by a missile attack.
The attack came amid an international wrangling about the allegations of the chemical weapons' use by the Syrian army in the attack on the rebels in the Douma district in the capital Damascus' Eastern Ghouta countryside.
Several loud explosions were heard in the early hours on Monday near the airfield in the eastern countryside of Homs. It was later confirmed to be a missile attack targeting the military facility.
The report later said the strike has caused casualties, but did not give exact numbers.
The Syrian air defense system acted against the attack, destroying eight missiles before they reached their target, while others hit the base, it said.
It was not immediately confirmed who was behind the attack, but state-run media outlets said the attack could have been carried out by the United States.
U.S. Pentagon spokesman Christopher Sherwood denied the report in a statement, saying the U.S. Department of Defense "is not conducting air strikes in Syria at this time."
U.S. 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 countryside near Damascus and the rebels there accused the government forces of using chlorine gas in an attack on Saturday that targeted the area.
The Syrian government denied the allegations, calling them fabrications.
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. The Islam Army also sent a batch of militants and fighters to the rebel-held city of Jarablus in northern Syria under the agreement.
Monday's missile strike is not the first foreign attack against Syria, as the United States targeted the Shayrat airbase in the countryside of Homs in April last year to punish alleged chemical weapons' use by the Syrian army on a rebel-held area in the northwestern province of Idlib.
The United States carried out that attack without waiting for results of investigation.
