A gas attack has reportedly taken place in Syria’s rebel-held Idlib, killing at least 58 people, with various media outlets reporting that a rocket has since hit a hospital treating the victims. The Syrian army has denied it was behind the attack.

The alleged attack in the town of Khan Sheikhoun reportedly killed at least 58 people, including 11 children under the age of eight, according to medical workers and the Britain-based Syrian Observatory for Human Rights, as cited by Reuters.

The head of Idlib's health authority, Mounzer Khalil, also said the attack killed more than 50 people and injured more than 300 others.

Videos posted online by activists claim to show the moment the bombs struck, with clouds of smoke rising into the air.

Locals said the alleged attack began in the early morning, when they heard planes in the sky followed by a series of loud explosions, after which people very quickly began to show symptoms, Al Jazeera reported.

Many of the victims were seen to be choking and fainting following the attack, and some had foam coming out of their mouths, according to medical sources who described the symptoms as related to a gas attack, as cited by media reports.

Pictures circulated by activists showed members of the volunteer White Helmets rescue group using hoses to wash down the injured, as well as two men with white foam around their mouths.

The pro-opposition Edlib Media Centre (EMC) also posted photos of people receiving treatment online, with some images showing what appeared to be the bodies of at least seven children in the back of a pick-up truck, France 24 reported.

Later a rocket slammed into a hospital treating the victims of the alleged gas attack, according to an AFP correspondent.

'Seriously concerned'

The Syrian National Coalition, an alliance of opposition groups, has accused President Bashar Assad's government of carrying out the gas attack and demanded a UN investigation.

The National Coalition demands the Security Council convene an emergency session...open an immediate investigation and take the necessary measures to ensure the officials, perpetrators and supporters are held accountable," the body said in a statement, as quoted by France 24.

The UN Commission of Inquiry on Syria said it is looking into the alleged gas attack, as well as the hospital attack, stressing that the use of chemical weapons and any deliberate targeting of medical facilities "would amount to war crimes and serious violations of human rights law."

"It is imperative for perpetrators of such attacks to be identified and held accountable," the commission said, as quoted by Reuters.

France has also called for an emergency UN Security Council (UNSC) meeting following the suspected attack, according to Reuters.

However, the UNSC will likely discuss the attack tomorrow, during a meeting which was previously scheduled, a correspondent for the Arabic-language Alhurra satellite television channel wrote on Twitter.

Diplomats: Security Council most likely to discuss chemical weapons attack in #Syria#KhanSheikhun tomorrow - Meeting was already scheduled — Nabil Abi Saab (@NabilAbiSaab) April 4, 2017

EU foreign affairs chief Federica Mogherini says the Syrian government bears responsibility for the alleged attack, calling it “awful.”

British Foreign Secretary Boris Johnson has also called for an investigation into the alleged attack, writing on Twitter that those responsible must be "held to account."

Horrific reports of chemical weapons attack in #Idlib#Syria. Incident must be investigated & perpetrators held to account — Boris Johnson (@BorisJohnson) April 4, 2017

Meanwhile, the Organisation for the Prohibition of Chemical Weapons (OPCW) wrote in a statement that it is "seriously concerned" by the alleged attack.

Turkey has called on the OPCW to immediately begin investigations into the reported attack, the country's foreign ministry said in a statement. The ministry also called on "all sides that influence the Syrian regime" to help put an end to alleged heavy ceasefire violations.

The Syrian army has denied allegations that it was behind the attack, despite allegations from the Syrian Observatory for Human Rights and other pro-opposition groups.

"We deny completely the use of any chemical or toxic material in Khan Sheikhoun town today and the army has not used nor will use in any place or time, neither in past or in future," the army said in a statement, as quoted by Reuters.

Earlier, a Syrian military source told Reuters that Damascus had not used chemical weapons, and dismissed the accusations as rebel propaganda.

The army "has not and does not use them, not in the past and not in the future, because it does not have them in the first place," the source said.

AFP also reported that a Syrian security source called the gas attack report a "false accusation."

“Based on the reports it might be that the Syrian Army targeted a place that was used as a chemical weapons factory or that stocked chemicals by the rebels,” Jamal Wakeem, a professor of history and international relations at the Lebanese University in Beirut, told RT.

Wakeem said he doesn’t believe the Syrian Army would be so “desperate” as to use chemical weapons, given the fact that it has been “achieving major success on various fronts.”

DETAILS: Syrian army strongly denies any involvement in alleged gas attack in Idlib, Syria https://t.co/TeSpNEV13Upic.twitter.com/LeHO0NmTuu — RT (@RT_com) April 4, 2017

He went on to state that although rebels have previously accused the Syrian government and Russian military of using chemical weapons, that news “turned out to be false,” noting that there was instead evidence that rebels had used chemical weapons in Syria and Iraq.

The Russian military said in a statement that it did not conduct any airstrikes in the Idlib Governorate.

Idlib province is largely controlled by an alliance of rebels, including Jabeh Fateh al-Sham, a former Al-Qaeda affiliate previously known as Al-Nusra Front.

Allegations of Damascus using chemical weapons were voiced by its opponents on several occasions.

The most-publicized incident happened in the eastern Ghouta neighborhood of Damascus in August 2013, a year after the Obama administration declared that a chemical weapons attack by the Syrian government would be a “red line,” after which Washington would use military force to intervene in the conflict.

The expected US bombing of the Syrian Army didn’t follow, and Russia defused the situation by convincing Damascus to join the Chemical Weapons Convention and destroying its arsenal. The development resulted in the Organization for the Prohibition of Chemical Weapons, the watchdog of the convention, winning the Nobel Peace Prize that year.

Even after the arsenal was destroyed, there were several occasions in which Damascus was accused of using less-potent chemicals such as chlorine gas as a weapon. The Syrian government denied all such accusations. The terrorist group Islamic State (IS, formerly ISIS/ISIL) reportedly used chlorine-filled shells against its enemies in Syria as part of its intimidation tactics.