06/04/2017 4:14 PM AEST | Updated 06/04/2017 6:14 PM AEST

This Father Lost His Entire Family In The Syrian Gas Attack

Both of his two nine-month-old twins and wife were killed.

Twitter/Sakir Khader
Abdel Hameed Alyousef also lost up to 20 other relatives in the attack.

Photos and footage have emerged on Wednesday of a Syrian father cradling his two 9-month-old twin children who were killed in the deadliest chemical weapons attack in the country since 2013, before taking them to a site to be buried.

Abdel Hameed Alyousef lost both Aya and Ahmed in the attack on the rebel-held town of Khan Sheikhoun in the Idleb province on Tuesday, as well as his wife and up to 20 other relatives including two brothers, two nephews, a niece and his sister-in-law, according to ABC News US.

In photos and video footage posted to social media, Alyousef can be seen stroking the twins' hair while they were draped in a white cloth before reportedly telling them "say goodbye, baby, say goodbye".

WARNING: This post includes graphic content that may disturb some readers

"I was right beside them. I took them outside with their mother... They were conscious, but 10 minutes later, we could smell [the gas], and my children couldn't handle it anymore. I left them to the medics and went to find my family," he said.

Syrian forces are suspected of being behind the attack which killed up to 72 civilians, despite the Syrian military having denied responsibility. In the hours following the attack, one of the medical clinics treating victims was hit by an airstrike.

Medics, activists and witnesses on the ground said that the air strikes caused people to suffocate, while others spasmed, went pale and gasped for air, according to British-based Syrian Observatory for Human Rights sources.

Witnesses say birds fell from the sky and dying children and adults were filmed foaming at the mouth.

The World Health Organisation (WHO) confirmed in a statement released on Wednesday the symptoms of those affected by the attack appear to show signs the chemicals used included deadly nerve agents banned by international law.

"The likelihood of exposure to a chemical attack is amplified by an apparent lack of external injuries reported in cases showing a rapid onset of similar symptoms, including acute respiratory distress as the main cause of death. Some cases appear to show additional signs consistent with exposure to organophosphorus chemicals, a category of chemicals that includes nerve agents," the statement read.

Prime Minister Malcolm Turnbull and Foreign Minister Julie Bishop have called for an independent, international investigation into the attack on Wednesday, condemning the "horrendous use of chemical weapons".

"If the Assad regime has used chemical weapons, as is being alleged, that constitutes a war crime. It constitutes a shocking war crime," Prime Minister Malcolm Turnbull told Tasmanian radio 7AD.

"The Assad regime should abide by the laws of armed conflict and there should be and will be I've no doubt, a full investigation into the circumstances of what appears to, well what has been, appears to be, a horrendous use of chemical weapons which we condemn."