President Barack Obama meets with Donald Trump, then the president-elect, in November. REUTERS/Kevin Lamarque President Donald Trump released a statement Tuesday blaming a chemical attack in Syria on the Obama administration's policies.

Dozens of people were reportedly killed on Tuesday when a hospital treating civilians injured in chemical attacks was bombed. Activists described the attack as among the worst in the country's six-year war.

"Today's chemical attack in Syria against innocent people, including women and children, is reprehensible and cannot be ignored by the civilized world," Trump said in a statement. "These heinous actions by the Bashar al-Assad regime are a consequence of the past administration's weakness and irresolution."

Trump cited President Barack Obama's inaction after issuing a "red line" in 2012 that suggested that the US would intervene militarily if the Assad regime used chemical weapons.

When evidence that Syrian forces had used chemical weapons to attack civilians emerged, the US declined to retaliate with military action, opting instead to broker a deal in which the Assad regime agreed to remove chemical weapons from Syria.

"President Obama said in 2012 that he would establish a 'red line' against the use of chemical weapons and then did nothing," Trump said. "The United States stands with our allies across the globe to condemn this intolerable attack."

But it doesn't appear that the Trump administration is planning to urge Assad to step down. And Trump didn't seem to want Obama to enforce the red line at the time, tweeting in 2013, "AGAIN, TO OUR VERY FOOLISH LEADER, DO NOT ATTACK SYRIA - IF YOU DO MANY VERY BAD THINGS WILL HAPPEN & FROM THAT FIGHT THE U.S. GETS NOTHING!"

Secretary of State Rex Tillerson told reporters while he was in Turkey last week that the "longer-term status" of Assad would "be decided by the Syrian people." And the US's ambassador to the UN, Nikki Haley, told reporters that the Trump administration's "priority is no longer to sit there and focus on getting Assad out."

The remark signaled a shift in America's official position on the Syrian strongman. Though they were criticized for failing to act against Assad, Obama and former Secretary of State John Kerry had long called for Assad to step down in a monitored transition of power.

Tillerson released a statement on the chemical attack on Tuesday, saying the US "strongly condemns" such actions.

"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 the statement, which stopped short of calling on Assad to relinquish power.

Tillerson instead shifted responsibility to Russia and Iran, two of Assad's biggest allies, saying they "bear great moral responsibility for these deaths."

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

Tillerson called on Russia and Iran to "exercise their influence over the Syrian regime and to guarantee that this sort of horrific attack never happens again."

Natasha Bertrand contributed to this report.