Syria's state news agency said airstrikes had been carried out against targets inside the country, and that there were casualties, the BBC reported Sunday night. The report said an airfield near Homs had been struck. Syria's news agency claimed eight missiles were shot down, the Associated Press reported. U.S. officials said it was not responsible, leading to speculation that they may have been carried out by Israel or France. "At this time, the Department of Defense is not conducting air strikes in Syria," the Pentagon said, according to a Reuters reporter, "However, we continue to closely watch the situation." Israel has struck Syrian targets at least three times in recent months. The apparent airstrikes came hours after reports that Syrian government forces used chemical weapons on civilians near Damascus, killing at least 49 people. In tweets Sunday morning, President Donald Trump warned Syria and its allies, Russia and Iran, that there would be a "big price to pay." Later Sunday, the U.S. and France promised a "strong, joint response" to the attack after Trump spoke to French President Emmanuel Macron. Last year, the U.S. launched missiles at a Syrian airbase after a chemical weapons attack.