Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE said Wednesday the Russian government needs to rethink its alliance with Syrian President Bashar Assad, the latest sign of a possible shift in the Trump administration's position.

Tillerson made clear that the U.S. believes the Syrian government is responsible for the deadly and destructive chemical attack that occurred Tuesday in northern Syria, taking dozens of lives, including many children.

“Well there is no doubt in our mind that the Syrian regime under the leadership of Bashar al-Assad is responsible for this horrific attack,” Tillerson told a room of reporters.

“And we think its time that the Russians really need to think carefully about their continued support of the Assad regime,” he added.

The Trump administration previously has not put pressure on Russia over Syria.

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Just days ago, Tillerson during a press availability in Turkey said Assad's status would be decided by the Syrian people. White House press secretary Sean Spicer last week said Assad's rule was a "political reality" the same day as Tillerson's remarks from Ankara.

But this stance seems to be changing after this week's chemical attack.

President Trump indicated Wednesday that this attack has made him rethink the White House’s Syrian policy.

Trump said the chemical attack “crossed a lot of lines for me.”

“It is very, very possible, and I will tell you it’s already happened, that my attitude toward Syria and Assad has changed very much,” the president added.

U.S. Ambassador to the United Nations Nikki Haley ripped Russia during a U.N. Security Council meeting, asking how long it would stand by and allow children to die in Syria.

Tillerson said in his statement on Wednesday that Syria’s allies — Russia and Iran — should “exercise their influence” over Assad to prevent another attack from occurring.

"Those who defend and support him, including Russia and Iran, should have no illusions about Assad or his intentions. Anyone who uses chemical weapons to attack his own people shows a fundamental disregard for human decency and must be held accountable,” Tillerson continued.

The Syrian government has denied responsibility for the attack, calling it a “heinous” crime and stressing their commitment to the Chemical Weapons Convention it joined in 2013.

The Russian government also said Wednesday the Syrian rebels carried out the attack, not the Syrian regime.

The attack took place in the northwestern Syrian town of Khan Sheikhoun.

Tillerson's comments come a week before he is scheduled to make a diplomatic visit to Moscow.