Leading Republican presidential candidate Donald Trump is making headlines again, after he called on Monday to block all Muslims from entering the United States.

Trump, who has previously called for surveillance against mosques and said he was open to establishing a database for all Muslims living in the United States, made the call in a news release in the wake of last week’s deadly mass shooting in San Bernardino, California.

“Without looking at the various polling data, it is obvious to anybody the hatred is beyond comprehension. Where this hatred comes from and why we will have to determine,” said Trump’s release, as quoted by CNN.

“Until we are able to determine and understand this problem and the dangerous threat it poses, our country cannot be the victims of horrendous attacks by people that believe only in Jihad, and have no sense of reason or respect for human life,” he added.

The release pointed to an online poll from the Center for Security Policy, which claimed that a quarter of Muslims living in the U.S. believe violence against Americans is justified as part of a global jihadist campaign.

Trump last month said he would consider closing some mosques in America with radical leadership if he were elected president.

His call came hours after the FBI said that Syed Farook and Tashfeen Malik, who carried out the attack in California last week, had been radicalized “for quite some time”.

It is believed Farook had contact with people from at least two terrorist organizations overseas, including the Al-Qaeda-affiliated Al-Nusra Front in Syria.

On Friday, it was reported that Malik had pledged allegiance to the Islamic State (ISIS) in a Facebook posting.

And on Sunday, Farook’s father told an Italian magazine his son was “obsessed” with Israel, shared ISIS ideology and wanted to see the establishment of an Islamic caliphate.