Footage has emerged that appears to show the aftermath of a chemical weapon attack in Syria.

The video, which was taken in a hospital and shows men and women frothing at the mouth and twitching from the effects of the nerve agent, was posted online just over a week ago.

The images were recorded at the medical facility in Afrin, about an hour’s drive from the city of Aleppo, where the alleged sarin attacks by the Bashar al Assad regime were carried out.

The British Foreign Office says it has "limited but persuasive evidence" the nerve agent sarin has been used.

The US says it believes "with some degree of varying confidence" chemical attacks have taken place.

Last month in Israel President Obama repeated his warning that if chemical weapons are used - he would take action:

The White House is now calling on the United Nations to conduct a comprehensive investigation into the matter. 

U.S senator John McCain wants intervention.

Ahmad Ramadan, a member of the Syrian National Coalition opposition group's executive body, called the U.S. assertion an "important step" that should be followed by actual measures taken by the U.N. Security Council and Friends of Syria group.

Ramadan told The Associated Press by phone from Istanbul that the U.S. has a "moral duty" to act to prevent President Bashar Assad from using more chemical weapons.

President Obama is expected to discuss the matter when he meets King Abdullah II of Jordan later today.