TEL AVIV, Israel — U.S. Defense Secretary Jim Mattis said Friday that Syria still possesses banned chemical weapons.

“I can say authoritatively that they have retained some,” said Mattis, who arrived earlier in Israel for talks with government leaders. “It’s a violation of the United Nations Security Council resolutions … and is going to have to be taken up diplomatically.”

Asked whether Syria has moved combat aircraft onto a Russian base in Syria, Mattis said, “No doubt they have dispersed their aircraft in recent days.” He did not elaborate.

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 at a news conference in Tel Aviv alongside Israeli Defense Minister Avigdor Lieberman. Later, the U.S. defense secretary was meeting with Prime Minister Benjamin Netanyahu.

Lieberman declined to comment on news reports that Israel believes Syria still holds between one ton and three tons of chemical weapons.