TEL AVIV, Israel — Syria still possesses chemical weapons, U.S. Defense Secretary Jim Mattis said in Israel on Friday, warning against the banned munitions being used again.

At a news conference in Tel Aviv, Mattis also said that in recent days the Syrian Air Force has dispersed its combat aircraft. The implication is that Syria may be concerned about additional U.S. strikes following the cruise missile attack earlier this month in retaliation for alleged Syrian use of sarin gas.

Mattis spoke alongside Israeli Defense Minister Avigdor Lieberman. “There can be no doubt in the international community’s mind that Syria has retained chemical weapons in violation of its agreement and its statement that it had removed them all,” said Mattis. He said he didn’t want to elaborate on the amounts Syria has in order to avoid revealing sources of intelligence.

“I can say authoritatively they have retained some, it’s a violation of the United Nations Security Council resolutions and it’s going to have to be taken up diplomatically and they would be ill advised to try to use any again, we made that very clear with our strike,” he said.