The White House on Tuesday confirmed a “reprehensible” and “intolerable” chemical attack had taken place in Syria and pinned the blame squarely on Bashar Assad’s regime.

White House spokesman Sean Spicer said US President Donald Trump had been briefed extensively on the attack, and suggested it was in the “best interest” of the Syrians for Assad not to lead the country.

“Today’s chemical attack in Syria against innocent people, including women and children, is reprehensible,” Spicer said, saying the administration was “confident” in its assessment that Assad was to blame.

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British Foreign Secretary Boris Johnson said the attack “bears all the hallmarks” of the Syrian government.

Johnson said in a statement Tuesday that he was “horrified” at the reports of the attack and said Assad’s government has repeatedly used chemical weapons in the past.

His comments followed reports from the Britain-based Syrian Observatory for Human Rights, which put the death toll from the attack at 58.

Johnson said his government “will continue to lead international efforts to hold perpetrators to account.”

French President Francois Hollande also blamed Syrian leader Assad for what he termed a “massacre.”

“Once again the Syrian regime will deny the evidence of its responsibility for this massacre,” Hollande said in a statement.

“Those who support this regime can once again reflect on the enormity of their political, strategic and moral responsibility,” Hollande added.

Despite the accusations, the Syrian military vehemently denied it was behind the strike.

“The army command categorically denies using any chemical or toxic substance in Khan Sheikhun today,” said a statement carried by the state news agency SANA.

“It stresses that it has never used them, any time, anywhere, and will not do so in the future,” it added.

The attack in the town of Khan Sheikhun left dozens struggling to breathe and displaying symptoms such as foaming at the mouth and vomiting and fainting, the Syrian Observatory for Human Rights said.

A hospital in the town where doctors were treating victims of the attack was also bombarded, an AFP correspondent said.

France called earlier Tuesday for an emergency meeting of the UN Security Council over the attack.

United Nations Syria envoy Staffan de Mistura also called for the perpetrators to be held accountable for the “horrific” attack.

De Mistura urged “clear identification of responsibilities and accountability.”

Speaking on the eve of a conference on Syria’s future, he said “every time we have a moment in which the international community is capable of being together — 70 countries tomorrow — there is someone, somehow, that tries to undermine that feeling of hope by producing a feeling of horror and outrage.”

But, he added, “we are not going to give up.”

The UN’s Commission of Inquiry for Syria said that it had begun investigating the incident.

“Reports suggesting that this was a chemical weapons attack are extremely concerning. The commission is currently investigating the circumstances surrounding this attack including the alleged use of chemical weapons,” said a statement from the UN experts who are probing potential war crimes committed during Syria’s civil war.

The condemnations followed those of others in the international community.

Turkish President Recep Tayyip Erdogan told his Russian counterpart Vladimir Putin in a phone call that the chemical weapons attack was “inhuman” and could endanger peace talks based in the Kazakh capital.

“President Erdogan said that this kind of inhuman attack was unacceptable and warned it risked wasting all the efforts within the framework of the Astana process” to bring peace to Syria, presidential sources said.

The sources did not indicate who was to blame for the attack, describing it as a “chemical weapons attack directed at civilians.”

Turkey has been a major foe of the Assad regime in Syria throughout the Syrian civil war, repeatedly accusing Damascus of war crimes. Russia has helped Assad by providing military and diplomatic support, including air strikes and ground forces.

But in the last months Ankara has deepened ties with Assad’s ally Russia, co-brokering a ceasefire that until now had drastically reduced the levels of violence.

Russia’s military said its planes did not carry out any strikes near Khan Sheikhun.

“Planes of the Russian air force have not carried out any strikes near Khan Sheikhun of Idlib province,” said a statement by the Russian defense ministry.

French Foreign Minister Jean-Marc Ayrault described the attack as “monstrous” and added: “I have called for an emergency meeting of the UN Security Council.”

Ayrault said “chemical weapons” had been used in the attack and that it was “more proof of the savagery that the Syrian people have been subjected to for so many years.”