'Islamic terrorism must be stopped'

US President Donald Trump on Friday said the world must use "whatever means necessary" to stop "radical Islamic terrorism," after twin attacks in Spain killed at least 14 people.

"Radical Islamic Terrorism must be stopped by whatever means necessary! The courts must give us back our protective rights. Have to be tough!" Trump said in one of his signature early morning tweet storms.

On Thursday, Trump courted controversy in the wake of the Barcelona van attack when he appeared to endorse the idea of mass executions for Islamist extremists. As justification, he alluded to a widely debunked account of summary punishment by a US general in the Philippines in the early 1900s.

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

He was referring to General John "Black Jack" Pershing who was the US governor of largely Muslim Moro province from 1909 to 1913. At the time, the Philippines was a US colony.

The debunked account -- which Trump has referred to in the past -- is as follows: Pershing's forces rounded up 50 Muslim insurgents and executed 49 of them with bullets dipped in pig's blood -- considered by Muslims to be unholy.

As the story goes, the 50th prisoner was released to tell his fellow fighters about what the Americans had done.

"And for 25 years, there wasn't a problem. Okay? Twenty-five years, there wasn't a problem," Trump said in February 2016 in South Carolina during a campaign rally.

Historians have expressed skepticism or outright denial that this event took place.