U.S. Secretary of State Rex Tillerson said on Wednesday that it is time for Russia to think carefully about its continued support for Syrian President Bashar Al-Assad.
The comments, quoted by Reuters, came in response to the chemical weapons attack in Idlib, which Tillerson blamed on Assad's forces.
"We think that it is time that the Russians really need to think carefully about their continued support of the Assad regime," the Secretary of State told reporters after a meeting with his Mexican counterpart at the State Department.
Meanwhile on Wednesday, U.S. officials rejected Russia's assertion that Syrian rebels were to blame for the attack rather than Assad.
U.S. intelligence officials, based on a preliminary assessment, said the deaths were most likely caused by sarin nerve gas dropped by Syrian aircraft on the town of Khan Sheikhoun on Tuesday.
Moscow claimed that the poison gas belonged to rebels and had leaked from an insurgent weapons depot hit by Syrian bombs.
A senior White House official, speaking on condition of anonymity, told Reuters the Russian explanation was not credible. "We don't believe it," the official said.
President Donald Trump condemned the chemical weapons attack in Idlib earlier on Wednesday, calling it a “horrible thing, unspeakable,” and “a terrible affront to humanity.”
“These are very troubled times in the Middle East,” he said at a press conference with Jordan’s King Abdullah.
“These heinous actions by the Assad regime cannot be tolerated. The United States stands with our allies across the globe to condemn this horrific attack,” added Trump.
On Tuesday, The White House blamed the Obama administration for creating conditions enabling the attack.
White House spokesman Sean Spicer told a briefing, "These heinous actions by the Bashar Al-Assad regime are a consequence of the last administration's weakness and irresolution. President Obama said in 2012 that he would establish a 'red line' against the use of chemical weapons and then did nothing."