BELGRADE, Serbia -- U.S. Sen. John McCain accused Russia on Monday of having cooperated with Syrian government forces in a chemical weapons attack that killed more than 80 people, including more than a dozen children.
The Republican senator from Arizona said at a news conference in Belgrade that he believes "the Russians knew about chemical weapons because they were operating exactly from the same base."
He said the U.S. launched cruise missile strikes last week against the Syrian base "in a response" to the chemical attack.
"I hope that this behavior by Syria, in what clearly is cooperation with Russia and Syria together, will never happen again," he said.
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McCain, speaking while on a tour of the western Balkans, the European region where Russia has been vying for increased influence, said the U.S. should take out Syria's air force as part of stopping Syrian President Bashar Assad from repeating such attacks in the future.
"I would prevent Bashar Assad from flying from his airfields if he doesn't renounce the use of these weapons," the former U.S. airman said. "The United States should first tell Russia that this kind of a war crime is unacceptable in the world today."
He said this week's visit by U.S. Secretary of State Rex Tillerson to Moscow should "lead to an agreement on the part of the Russians that they will not allow Syria to ever again use chemical weapons."
"Remember, Russians made that commitment after [Syrian government forces] crossed the so-called red line back [in the past]. I hope that this will be the first item on the agenda," McCain said.
There was no immediate comment from Moscow on McCain's statement. The Kremlin has repeatedly said the civilian exposure to toxic agents resulted from Syrian warplanes hitting a rebel ammunition warehouse on the eastern outskirts of the village of Khan Sheikhoun.
McCain is not the only one calling Russia complicit in the Syria attack.
A senior U.S. official who demanded anonymity said Monday that the U.S. had reached the conclusion Russia knew in advance of Syria's chemical weapons attack.
A drone operated by Russians was flying over a hospital as victims of the attack were rushing to get treatment, the official said. Hours after the drone left, the official said, a Russian-made fighter jet bombed the hospital in what American officials believe was an attempt to cover up the usage of chemical weapons.
The official said the U.S. has no proof of Russian involvement in the chemical attack but that the presence of the surveillance drone over the hospital couldn't have been a coincidence and Russia must have known the chemical weapons attack was coming.
The official, who wasn't authorized to speak publicly on intelligence matters, didn't give precise timing for when the drone was in the area. The official also didn't provide details for the military and intelligence information that form the basis of what the Pentagon was said to now believe.
Another U.S. official cautioned that no final American determination has been made that Russia knew ahead of time that chemical weapons would be used. That official wasn't authorized to speak about internal administration deliberations and spoke on condition of anonymity.
Although Russia has steadfastly supported Assad's government, and they've coordinated military attacks together, Washington has never accused Moscow of complicity in any attack that involved the gassing of innocent civilians, including children. The former Cold War foes even worked together in 2013 to remove and destroy more than 1,300 tons of Syrian chemical weapons and agents.
Until Monday, U.S. officials had said they weren't sure whether Russia or Syria operated the drone. The senior official said the U.S. is now convinced that Russia controlled the drone. The official said it still isn't clear who was flying the jet that bombed the hospital because the Syrians also fly Russian-made aircraft.
U.S. officials previously have said Russians routinely work with Syrians at the Shayrat air base where the attack is supposed to have originated. U.S. officials also have said the chemical weapons were stored there.
Last Thursday, 59 Tomahawk missiles were fired on the government-controlled base in the United States' first direct military action against Assad's forces.
The U.S. has been focusing its military action in Syria on defeating the Islamic State extremist group.
On Monday, Col. John Thomas, a U.S. military spokesman, said the U.S. had taken extra defensive precautions in Syria in case of possible retaliation against American forces for the cruise missile attack.
Thomas told reporters at the Pentagon that the increased emphasis on defensive measures to protect U.S. troops on the ground in Syria led to a slight and temporary decline in offensive U.S. airstrikes against the Islamic State in Syria.
There has been no Syrian retaliation so far for the cruise missile attack, which destroyed or rendered inoperable more than 20 Syria air force planes, he said.
Thomas said the U.S. intends to return to full offensive air operations against the Islamic State as soon as possible.
Barrel bombs on U.S. list
Also Monday, White House spokesman Sean Spicer warned Syria to stop using barrel bombs against civilians, suggesting that President Donald Trump may expand the criteria for U.S. action against Assad's forces.
"If you gas a baby, if you put a barrel bomb into innocent people, I think you can -- you will see a response from this president," Sean Spicer told reporters at his daily briefing on Monday. "That is unacceptable."
Trump ordered a missile attack last week on a Syrian air base, citing Syria's use of chemical weapons. Because Assad's forces depend more heavily on barrel bombs in quelling opposition in the civil war, the stance increases the likelihood of additional U.S. intervention in Syria.
Another administration spokesman tempered Spicer's comments after the briefing. Michael Short said "nothing has changed in our posture. The president retains the option to act in Syria against the Assad regime whenever it is in the national interest, as was determined following that government's use of chemical weapons against its own citizens."
The Syrian government dropped at least 12,958 barrel bombs in 2016, resulting in the deaths of at least 653 civilians, according to the Syrian Network for Human Rights. The United Nations Security Council demanded Assad stop using barrel bombs in a February 2014 resolution, and a U.N. inquiry commission found the government's use of the crude weapons violated international law.
The improvised bombs, which are typically simple large containers packed with gasoline and shrapnel thrown out of helicopters or other aircraft, indiscriminately target the civilian population in the urban areas in which Assad's forces have used them, human-rights groups have reported.
Spicer emphasized Monday that further U.S. attacks on Syria remain a possibility, pledging decisive and proportional responses to actions deemed unacceptable by Trump. But Spicer declined to elaborate further on what actions may provoke a U.S. military strike.
"The president's been very clear that he's going to keep his cards close to his vest, but make no mistake, he will act," Spicer said.
Information for this article was contributed by Dusan Stojanovic, Robert Burns and Lolita C. Baldor of The Associated Press and by Justin Sink of Bloomberg News.
A Section on 04/11/2017