Trump, speaking alongside Jordan’s King Abdullah II in the Rose Garden, offered no details about what steps the US might take in response.

Decrying an “affront to humanity,” President Donald Trump declared Wednesday that a chemical weapons attack in Syria “cannot be tolerated” but did not say what the US might do in response. He blamed the attack squarely on Syrian President Bashar Assad.

Trump, speaking alongside Jordan’s King Abdullah II in the Rose Garden, offered no details about what steps the US might take in response, even as his UN ambassador, Nikki Haley, was promising a strong and perhaps even unilateral response. But Trump said the attack was “so horrific” and noted that it had killed “innocent people, small children and even beautiful little babies.”

“These heinous actions by the Assad regime cannot be tolerated,” Trump said.

He said the US stood with its global allies “to condemn this horrific attack.”

The United States and Russia were trading conflicting assertions Wednesday about who launched a chemical weapons attack in Syria that killed 72 people, as world leaders grasped for a response to the latest atrocity in Syria’s intractable civil war.

As Trump stood by his charge that Assad’s forces were responsible, Russia disagreed. The staunch Assad ally insisted that the chemicals were dispersed when Syrian warplanes bombed a facility where rebels were building chemical weapons.

At the United Nations, Trump’s envoy threatened unilateral US action if the world body failed to act.

“When the United Nations consistently fails in its duty to act collectively, there are times in the life of states that we are compelled to take our own action,” Haley declared. She addressed an emergency meeting of the Security Council, which was weighing a resolution condemning chemical weapons use in Syria. Russia, which has veto power, is opposed.

Yet in Moscow, Russian Foreign Ministry spokeswoman Maria Zakharova focused her attention elsewhere: “It’s necessary to demand that the rebels offer full access to study the area and collect necessary information.”

Leaders and officials in other countries, including Britain and Israel, joined the US in saying Assad’s forces were responsible.

A US official said an American review of radar and other assessments showed Syrian aircraft flying in the area at the time of the attack. Russian and coalition aircraft were not there at that time, said the official, who wasn’t authorized to discuss intelligence publicly and requested anonymity. Washington hasn’t yet concluded what type of chemical was used.

On Tuesday, President Donald Trump split the blame between Syria’s embattled leader and former President Barack Obama for the country’s worst chemical weapons attack in years.

While calling the attack “reprehensible” and intolerable, Trump said Obama “did nothing” after Assad crossed the former US leader’s “red line” in 2013.

“These heinous actions by the Bashar al-Assad regime are a consequence of the past administration’s weakness and irresolution,” Trump said.

The political tone of Trump’s statement took many US officials by surprise. They noted that US presidents have rarely attacked their predecessors so aggressively for events like chemical weapons attacks that Democrats and Republicans both abhor.

Several officials involved in internal administration discussions said Trump’s National Security Council had been preparing a different statement, until the president’s closest advisers took over the process. The officials weren’t authorized to speak publicly on the matter and demanded anonymity.

The president’s eldest daughter and top adviser, Ivanka Trump, took a more compassionate tone, tweeting Wednesday, “Heartbroken and outraged by the images coming out of Syria following the atrocious chemical attack yesterday.”

At least 72 people died in the town of Khan Sheikhoun. The World Health Organization said victims seemed to show symptoms consistent with nerve agent exposure. Videos from the scene showed volunteer medics using firehoses to wash the chemicals from victims’ bodies and lifeless children being piled in heaps.

President Donald Trump, accompanied by first lady Melania Trump and Queen Rania, shakes hands with Jordan’s King Abdullah II in the Oval Office of the White House in Washington, Wednesday, April, 5, 2017.