A suspected chemical weapons attack in Syria on Tuesday killed scores of civilians — including children — and drew an international outcry on the eve of a global conference to discuss the future of the beleaguered, war-weary nation.

The Syrian Observatory for Human Rights, a U.K.-based monitoring group, said 58 people were killed in the town of Khan Sheikhoun in northern Idlib province, including 11 children. The  death toll is likely to rise, the group said.

Turkey said it had dispatched 30 ambulances to Idlib following chlorine gas attacks in the northwestern province, the Turkish Anadolu news agency reported. Syrian opposition health minister Firas Jundi put the death toll at more than 100 civilians and said 500 others, mostly children, were affected by the gas.

"I believe this horrible memory will stay with me for the rest of my life," Jundi told CNN.

The Syrian anti-government activist group Idlib Media Center published photos of young children receiving medical treatment, and a video showed what appeared to be bodies of children lined up on a blanket. The Syrian government of President Bashar Assad denied using chemical weapons, the Syrian Arab News Agency reported. But the U.S. and international communities were unconvinced.

White House spokesman Sean Spicer said the attack was "reprehensible and cannot be ignored by the civilized world," blaming the Obama administration in part for "weakness and irresolution" toward Syria. Spicer said the Trump administration was assessing what action it would take.

"Another vicious chemical attack in #Syria - how do the Syrian people determine their own future while they are being slaughtered?" tweeted Sen. John McCain, chairman of Senate Armed Services Committee. Secretary of State Rex Tillerson had said last week that ousting Syrian President Bashar Assad's future "will be decided by the Syrian people." The Trump administration has consistently stressed its priority of defeating the Islamic State.

France, which supports U.S.-backed rebels in Syria, called for a special meeting of the U.N. Security Council. British Foreign Minister Boris Johnson said he was "horrified" by the attack that "bears all the hallmarks" of chemical weapons previously used by the Syrian regime. Turkish President Recep Tayyip Erdogan called the attack "inhuman" and "unacceptable" in a call Tuesday to Russian President Vladimir Putin, Erdogan's office said.

International human rights organization Amnesty International said the reports of Tuesday's attack "are alarming and must be urgently investigated."

Ahmet Üzümcü, who leads the Organization for the Prohibition of Chemical Weapons, said his group was gathering and analyzing information.

Syrian forces loyal to Assad have been involved with chemical weapons before in the brutal six-year civil war against U.S-backed rebels. Üzümcü's agency implemented a 2013 agreement reached by the U.S. and Russia in 2013 to destroy Syria's chemical weapons arsenal.

Last year, the United Nations issued a report accusing Syria of using internationally banned toxic chemical weapons on civilians in 2014 and 2015.

Representatives from more than 50 nations are gathering in Brussels for a conference Wednesday to discuss the financial and humanitarian needs of Syria. The United Nations estimates that 13.5 million people needing humanitarian assistance, including 4.7 million people living in besieged or hard to reach areas.