Separately, Syrian state-run TV station al-Ikhbariya cited its Deir al-Zor correspondent as saying coalition warplanes had destroyed a building in al-Mayadeen used as a prison by Islamic State to hold a "large number of civilians". ISIS' meteoric rise, however, was primarily an outcome of two failed states in the heart of the Middle East-Iraq and Syria-and the marginalization of Sunni communities in Iraq's al-Anbar province and Syria's rural areas. Mattis said as he traveled to Europe for meetings with defense ministers at North Atlantic Treaty Organisation.
Mattis also said that as the fight against ISIS grows more complex and moves into the Euphrates River Valley, it will require more deconfliction with the Russians.
Reporters traveling in Germany with the United States defence secretary, James Mattis, were told that the Pentagon was prepared to take action after activity was seen at the Shayrat base similar to the pattern that preceded the April gas attack on Khan Sheikhoun, which killed at least 80 people. Still, on June 18, a U.S. Navy F/A-18E Super Hornet shot down a Syrian Sukhoi Su-22 bomber that attacked U.S. -backed rebel forces. It will require rigorous communication through the several channels that the United States and Russian Federation have established to avoid getting tangled in Syria's civil war.
"When they don't need certain things any more, we'll replace those with something they do need", said Mattis, who is expected to meet with his Turkish defense counterpart during a North Atlantic Treaty Organisation meeting later this week in Brussels.
But Mattis said the de-confliction talks continue and are happening at several military levels, to insure that aircraft and ground forces are safe. Yet changes in the US military's war on ISIS, with US President Donald Trump transferring more authority over such operations to the Pentagon, have increased civilian deaths.
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"If we are responsible for any civilian casualties we come forth and admit it", he said.
The regime denied any use of chemical weapons.
It depends, he said, on the battle and what weapons the Kurdish fighters need.
The Syrian Observatory for Human Rights says at least 42 people were killed, identifying them as prisoners of Islamic State.
In addition to the White House threat, a spate of incidents in recent weeks - including the downing of a Syrian government jet and two Iranian-made drones by USA aircraft - appear to suggest the opposite of Mattis's claims.