As Tillerson landed in Moscow, senior White House officials briefed reporters on declassified US intelligence they said disproved Russia's claim that rebels were responsible for the chemical weapons.
Also speaking at the ceremony in Italy, Federica Mogherini, EU foreign-policy chief, said "there is no military solution to this war, and the negotiations in Geneva must start again with the support of all of us: Europe is the one which is trying to get the Syrians to sit at the same table". The area around the hospital showed impact craters on April 6, the officials said, which were consistent with a traditional bomb.
A deadly chemical attack in Syria has prompted rising tensions over the future of the regime of President Bashar Assad.
Among those were that the chemical weapons belonged to rebel or terrorist groups opposed to the Assad regime. That official wasn't authorized to speak about internal administration deliberations and spoke on condition of anonymity.
The allegation of Russian foreknowledge is grave, even by the standards of the now dismal U.S.
During a televised press conference, Mr. Putin said unnamed provocateurs throughout Syria are looking execute chemical attacks against anti-government and civilian targets, and lay the blame on the Assad regime, Agence France Presse reported. "But the fact that someone would strike the hospital - potentially to hide the evidence of a chemical attack ... is a question that we are very interested in".
The number of civilians the Syrian Network for Human Rights says have been killed by US -led coalition forces in Syria, as recently as March 18. United States agencies are investigating Russia's alleged role in trying to influence last year's U.S. election, complicating efforts to find common ground in tackling ISIL.
The Syrian government has denied it was behind the April 4 assault which killed as many as 100 people.
US officials previously have said Russians routinely work with Syrians at the Shayrat air base where the attack is supposed to have originated.
SYRIA OPPOSES: President Bashar al-Assad's office denounced the US strike as 'reckless, irresponsible behavior'.
Washington's missile strike was the first time it had intervened directly against the regime of Assad, who is fighting a civil war with the backing of Russian Federation and Iran.
The U.S. has been focusing its military action in Syria on defeating the Islamic State group.
Thomas told reporters at the Pentagon that the increased emphasis on defensive measures to protect US troops on the ground in Syria led to a slight and temporary decline in offensive USA airstrikes against IS in Syria.
The Trump administration's change of heart, apparently spurred in part by the president's emotional response to the images of chemical weapons victims, also is serving another goal: defanging the perception of coziness between Trump and Moscow.