"We have to be very strong with our military, with our security. We have to be extremely strong," Trump said during a phone interview on "Fox and Friends."

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"We have to be very strong in terms of looking at the mosques, you know, which a lot of people say, 'Oh, we don't want to do that. We don't want to do that.' We're beyond that."

Trump similarly called for domestic surveillance of mosques in the U.S. after the Paris attacks in November 2015. He has since claimed the title of being the presumptive Republican presidential nominee.

"That man yesterday was sick with hate," Trump said, referring to Omar Mateen, the U.S. citizen authorities said carried out the shooting, which left 49 dead and more than 50 wounded or injured.

Mateen reportedly called 911 to claim allegiance to the Islamic State in Iraq and Syria's (ISIS) leader before carrying out the attack, which has been called the deadliest mass shooting in U.S. history.

"You have many, many people, thousands of people, already in our country, that are sick with hate. And people that are around him, Muslims, know who they are, largely. They know who they are. They have to turn them in," Trump said, referring to last year's San Bernardino, Calif., attackers.