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 on Tuesday urged Russia and Iran to prevent Syrian President Bashar Assad from launching chemical weapons attacks following a deadly chemical attack in Syria.

"While we continue to monitor the terrible situation, it is clear that this is how Bashar al-Assad operates: with brutal, unabashed barbarism," Tillerson said in a statement.

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

The top U.S. diplomat urged Iran and Russia to commit to a peace agreement in the region and to "exercise their influence" over Assad to prevent future chemical attacks.

"It is also clear that this horrific conflict, now in its seventh year, demands a genuine ceasefire and the supporters of the armed combatants in the region need to ensure compliance," Tillerson said.

"We call upon Russia and Iran, yet again, to exercise their influence over the Syrian regime and to guarantee that this sort of horrific attack never happens again. As the self-proclaimed guarantors to the ceasefire negotiated in Astana, Russia and Iran also bear great moral responsibility for these deaths."

The White House on Tuesday also condemned the chemical attack, with President Trump calling it "reprehensible" and stating that it "cannot be ignored by the civilized world."

At the same time, Trump blamed the "heinous actions" of Assad's regime on the Obama 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. The United States stands with our allies across the globe to condemn this intolerable attack," Trump said.

Trump didn't say how his administration would respond to the attack, considered the worst chemical weapons strike in Syria in years.

The strike carried out in the rebel-held area of Idlib Province reportedly killed dozens of people, including children, and injured more.

Moscow has consistently defended the Assad regime in Syria, and has argued that removing the Syrian leader from power would only further destabilize the region.