A suspected chemical attack in a rebel-held Syrian town killed 72 people and injured 400 others Tuesday, a medical relief group said, and some medics treating the wounded were later struck by rubble when an aircraft reportedly bombed a hospital.

A hospital in Syria's northern Idlib province was hit soon after the area was bombarded with a suspected chemical agent, an AFP correspondent reported.

The U.N. Security Council is to convene for an emergency meeting over the suspected deadly chemical attack. At least 11 of the 72 people that were reported killed were children.

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

Organization for the Prohibition of Chemical Weapons says it is examining allegations of at least 8 gas attacks in Syria since start of 2017 https://t.co/Wt0kb31kld — Fox News Research (@FoxNewsResearch) April 4, 2017

Secretary of State Rex Tillerson reacted, "While we continue to monitor the terrible situation, it is clear that this is how Bashar al-Assad operates: with brutal, unabashed barbarism. Those who defend and support him, including Russia and Iran, should have no illusions about Assad or his intentions. Anyone who uses chemical weapons to attack his own people shows a fundamental disregard for human decency and must be held accountable."

Mohammed Rasoul, the head of a Syrian ambulance service, told the BBC that first responders found people choking in the streets.

"Our team is still there, moving patients from one place to another because of overcrowded hospitals," he said. "I am speaking to my team and they are doing fine, but the situation over there is very bad and most of those who are suffering are children."

The media center published footage of medical workers appearing to intubate an unresponsive man stripped down to his underwear and hooking up a little girl foaming at the mouth to a ventilator.

There was no comment from the government in Damascus or any international agency in the immediate aftermath of the attack.

It was the third claim of a chemical attack in just over a week in Syria. The previous two were reported in Hama province, in an area not far from Khan Sheikhoun, the site of Tuesday's alleged attack.

Tuesday's reports came on the eve of a major international meeting in Brussels on the future of Syria and the region, to be hosted by the EU's High Representative Federica Mogherini.

The Syrian American Medical Society, which supports hospitals in opposition-held territory, said it had sent a team of inspectors to Khan Sheikhoun before noon and an investigation was underway.

German Foreign Minister Sigmar Gabriel has called on Russia to endorse a planned United Nations Security Council resolution condemning a suspected chemical weapons attack in Syria.

Gabriel said Wednesday in Brussels before the opening of the international conference on the Syria conflict that, "We appeal to Russia to approve this resolution, to investigate this case and to bring to justice those who are responsible."

The Syrian activists had no information on what agent could have been used in the assault. They claimed the attack was caused by an airstrike carried out either by the Syrian government or Russian warplanes.

Ahmed al-Sheikho, of the Idlib Civil Defense team, says the strikes did not cause any casualties because the area had been evacuated following Tuesday's attack.

Mohammed Hassoun, a media activist in nearby Sarmin -- also in Idlib province where some of the critical cases were transferred -- said the hospital there is equipped to deal with such chemical attacks because the town was also struck, early on in the Syrian uprising. The Sarmin hospital is about 31 miles away from the scene of the attack.

"Because of the number of wounded, they have been distributed around in rural Idlib," he told The Associated Press by phone. "There are 18 critical cases here. They were unconscious, they had seizures and when oxygen was administered, they bled from the nose and mouth."

Hassoun, who is documenting the attack for the medical society, said the doctors there have said it is likely more than one gas.

"Chlorine gas doesn't cause such convulsions," he said, adding that doctors suspect sarin was used.

Hussein Kayal, a photographer for the Idlib Media Center, said he was awoken by the sound of a bomb blast around 6:30 a.m. When he arrived at the scene there was no smell, he said.

He found entire families inside their homes, lying on the floor, eyes wide open and unable to move. Their pupils were constricted. He put on a mask, he said. Kayal said he and other witnesses took victims to an emergency room, and removed their clothes and washed them in water.

He said he felt a burning sensation in his fingers and was treated for that.

A Turkey-based Syrian man whose niece, her husband and one-year-old daughter were among those killed, said the warplanes struck early, as residents were still in their beds. He spoke on condition of anonymity because he feared for the safety of family members back in Syria.

The province of Idlib is almost entirely controlled by the Syrian opposition. It is home to some 900,000 displaced Syrians, according to the United Nations. Rebels and opposition officials have expressed concerns that the government is planning to mount a concentrated attack on the crowded province.

Claims of chemical weapons attacks, particularly the use of the chlorine agent, are not uncommon in Syria's conflict. The worst attack was what a U.N. report said was an attack by toxic sarin gas in August 2013 on the Damascus suburb of Ghouta that killed hundreds of civilians.

The Syrian Coalition, an opposition group based outside the country, said government planes carried out the airstrike on Khan Sheikhoun, south of the city of Idlib, the provincial capital.

It said the planes fired missiles carrying poisonous gases, killing dozens of people, many of them women and children. The coalition described the attack as a "horrifying massacre."

Photos and video emerging from Khan Sheikhoun show limp bodies of children and adults. Some are seen struggling to breathe; others appear foaming at the mouth.

A medical doctor going by the name of Dr. Shajul Islam for fears for his own safety said his hospital in Idlib province received three victims, all with narrow, pinpoint pupils that did not respond to light. He published video of the patients on his Twitter account.

Pinpoint pupils, breathing difficulties, and foaming at the mouth are symptoms commonly associated with toxic gas exposure.

The opposition's Civil Defense search-and-rescue group, which released photos showing paramedics washing down victims, has not published a casualty toll.

The activist-run Assi Press published video of paramedics carrying victims from the scene by a pickup truck. The victims were stripped down to their underwear. Many appeared unresponsive.

The New York-based Human Rights Watch has accused the Syrian government of conducting at least eight chemical attacks using chlorine gas on opposition-controlled residential areas during the final months in the battle for Aleppo last year that killed at least nine civilians and injured 200.

Also, a joint investigation by the United Nations and the international chemical weapons watchdog determined the Syrian government was behind at least three attacks in 2014 and 2015 involving chlorine gas and the Islamic State group was responsible for at least one involving mustard gas.

The Associated Press contributed to this report.