Syria still possesses chemical weapons, the Pentagon chief has said, in a fresh US warning against the banned munitions being used again.
Speaking in Tel Aviv on Friday during a visit to Israel, James Mattis said that in recent days the Syrian air force has dispersed its combat aircraft.
The implication is that Syria may be concerned about additional US air strikes following the cruise missile attack earlier this month in retaliation for alleged Syrian use of sarin gas.
"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," Mattis said.
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The US defence secretary said he did not want to elaborate on the amounts Syria possesses in order to avoid revealing intelligence sources.
"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," said Mattis.
Israeli defence officials said this week that Syria still has up to three tonnes of chemical weapons in its possession.