House Speaker Paul Ryan said the nation can’t back down against Islamist extremism following the attack at a gay nightclub Sunday killing 50 and injuring 53.

Islamic State has taken credit for the murders, which were committed by Omar Mateen, a U.S. citizen raised in New York.

“As we heal, we need to be clear-eyed about who did this. We are a nation at war with Islamist terrorists,” Ryan said in a statement. “Theirs is a repressive, hateful ideology that respects no borders.”

The speaker’s office announced Sunday afternoon Ryan called for the flags to be lowered over the Capitol in remembrance of the victims.

“It is a threat to our people at home and abroad,” he continued. “Our security depends on our refusal to back down in the face of terror. We never will.”

Florida Sen. Marco Rubio said he fears there will be other attacks like it, calling homegrown violent extremists the biggest threat to the nation.

Mateen was raised in the United States, but had pledged his allegiance to ISIS in a 911 call ahead of the mass shooting.

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