A suspected Syrian Government chemical attack has killed scores of people, including children, in the north-western province of Idlib, according to observers and medical officials on the ground.

Key points: US, UK condemn attack as demonstrative of President Assad's "barbarism"

US, UK condemn attack as demonstrative of President Assad's "barbarism" Syria's Foreign Ministry denies military was responsible for the attack

Syria's Foreign Ministry denies military was responsible for the attack Emergency UN Security Council meeting is called for talks on the strike

The attack caused many people to choke or faint, and some had foam coming out of their mouths, the Syrian Observatory for Human Rights said, citing medical sources who described it as a sign of a gas attack.

"I was asleep when the warplane hit us," said one victim, a young boy, from a nearby hospital.

"I went outside with dad, but my head started hurting. I fell asleep and woke up to find myself here."

Following the initial suspected gas attack, medical officials on the ground reported that aircraft were also firing rockets at the hospitals treating survivors.

The head of the health authority in rebel-held Idlib said more than 50 people had been killed and 300 injured in the attacks, while the Syrian Observatory for Human Rights said the attacks killed at least 58 people and was believed to have been carried out by Syrian Government jets.

Video posted online by opposition activists showed the lifeless bodies of children laid out on the back of a truck, and activists circulated pictures showing a reported victim with foam around his mouth and rescue workers hosing down almost naked children squirming on the floor.

If confirmed, the incident reported in the town of Khan Sheikhoun would be the deadliest chemical attack in Syria since sarin gas killed hundreds of civilians in Ghouta near Damascus in August 2013.

Firas al-Jundi, a health official with the opposition-aligned Idlib medical council, said the symptoms were consistent with a gas attack.

"The symptoms were clear on the patients, suffocation, respiratory failure, foaming at the mouth, loss of consciousness, convulsions and paralysis," he said.

"These symptoms usually appear as a result of poisonous gas leading to convulsions in body."

Trump says 'reprehensible' attack can't be ignored

Sorry, this video has expired Patients are brought into hospitals suffering symptoms of a suspected gas attack. (Photo: Reuters/Ammar Abdullah)

US President Donald Trump called the assault "reprehensible" and one that "cannot be ignored by the civilised world," rhetoric that harkened back to Barack Obama's criticism in 2013 of an earlier chemical attack ascribed to President Bashar Assad's forces.

Mr Trump said Mr Assad was responsible for the latest deaths, yet also targeted his predecessor's failed strategy to deter such attacks.

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

It was a clear reference to four years ago, when Mr Obama failed to deliver on his "red line" when he didn't authorise military action against Mr Assad in response to a sarin gas attack that killed hundreds outside Damascus.

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

Mr Trump left it to his top diplomat, Secretary of State Rex Tillerson, to assign culpability to Russia and Iran, Mr Assad's most powerful allies.

Mr Tillerson noted both countries signed up as guarantors to a recent Syrian ceasefire and said they must pressure Mr Assad to cease operating with "brutal and unabashed barbarism"

British Prime Minister Theresa May also condemned the attack in a video statement, adding that Mr Assad had has no future in a "stable" Syria.

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"I'm very clear that there can be no future for Assad in a stable Syria which is representative of all the Syrian people," Ms May said.

"I call on all the parties involved to ensure we have a transition away from Assad ... we cannot allow this suffering to continue."

Syrian military has no chemical weapons: Foreign Ministry

Sorry, this video has expired Journalist captures moment airstrike hits Khan Shaykhun hospital

Damascus has repeatedly denied using any such weapons but the United Nations has accused both the regime and opposition forces of staging chemical attacks.

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Syria's Armed Forces and Military General Command said it did not use chemical weapons against civilians, saying it was too "honourable" to carry out such "heinous" crimes.

Syria's Foreign Ministry said Damascus was committed to its obligations under the Chemical Weapons Convention it joined in 2013.

In comments to the official news agency SANA, a Foreign Ministry official said the country's military had no chemical weapons of any type and had "not used them before or later and doesn't seek to acquire them".

Russia also denied involvement in the attack.

The United Nations Security Council was to meet on Wednesday, at the request of Britain and France, to discuss the attack.

Attack kills dozens, destroys medical centre, rescue vehicles

Pro-opposition Orient News television said the strikes had killed 50 people and injured more than 150.

The head of the opposition's civil defence force in Khan Sheikhoun, Idlib province, said a medical centre was levelled and five rescue vehicles damaged in a strike hours later.

Warplanes "targeted us after the attack", said the man, who goes by the name of Aby Hamdu, adding it was not clear if anyone was killed.

France's Foreign Minister on Tuesday called for an emergency meeting of the United Nations Security Council after the suspected gas attack.

"A new and particularly serious chemical attack took place this morning in Idlib province. The first information suggests a large number of victims, including children. I condemn this disgusting act," Jean-Marc Ayrault said in a statement.

"In the face of such serious actions that threaten international security, I ask for everyone not to shirk their responsibilities. With this in mind, I ask for an emergency meeting of the UN Security Council."

ABC/Wires