Donald Trump resurrects discredited pigs' blood fable in Barcelona terror aftermath

US President Donald Trump has responded to a violent terror attack in Barcelona by implying that Spanish authorities ought to dip their bullets in pigs' blood before firing at Islamic militants.

The attack saw a man drive a truck into a group of pedestrians, leaving at least 13 dead and as many as 80 people hospitalised.

The remark, made in the form of a post on the former reality TV star's Twitter account, is based on a now-debunked story about a US general in the early 1900s.

"The United States condemns the terror attack in Barcelona, Spain, and will do whatever is necessary to help. Be tough & strong, we love you!" he wrote in an initial tweet, before continuing on.

"Study what General Pershing of the United States did to terrorists when caught. There was no more Radical Islamic Terror for 35 years!"

A legend has been doing the rounds for years that General John J Pershing dipped bullets in pigs' blood and buried Islamic extremists in pig skins or alongside pig corpses, in an effort to discourage further terror attacks in the Philippines.

Pigs are deemed unclean animals in Islamic texts, and some believe that contact with it, particularly in death, prevents souls entering into heaven or receiving spiritual rewards.

However, the tale has since been thoroughly debunked, with historical accounts of General Pershing recognising him as a deeply empathetic man who preferred to force enemies to surrender rather than kill them.

Other accounts say General Pershing only ever threatened to kill Muslims, but never did so himself - and was often apologetic when his soldiers brought about their death.

It's not the first time President Trump has referred to the fable to make a point about dealing to terrorists swiftly and effectively. In April 2016, he told the dubious tale at a rally in California, while he was on the campaign trail.

Mr Trump has also drawn criticism for referring to the incident in Barcelona as a terror attack so quickly, while refusing to label a similar vehicle attack at a recent rally in Charlottesville, Virginia as terrorism.