The mass shooting in Las Vegas is "heartbreaking news" and the tragedy "horrifies us all," House Speaker Paul Ryan said on Monday after 50 were killed and over 400 were wounded during an outdoor concert on the Las Vegas Strip.

"America woke up this morning to heartbreaking news. This evil tragedy horrifies us all," Ryan said in a statement. "To the people of Las Vegas and to the families of the victims, we are with you during this time. The whole country stands united in our shock, in our condolences, and in our prayers."

Ryan's office also announced that flags on the Capitol grounds will fly at half-staff.

Moments before Ryan's made his statement, the Islamic State claimed responsibility for the attack and said that the shooter, Stephen Craig Paddock, had converted to Islam months earlier.

House Minority Leader Nancy Pelosi, D-Calif., struck a similar chord as Ryan, saying that the mass shooting will not "break our spirits."

"It is particularly despicable that this attack was carried out during a concert, transforming an evening of music and celebration into a heartbreaking and horrific night of violence," Pelosi said. "Our nation will never allow fear and violence to bow us or break our spirits.

"America will never waver in its love and support for the people of Las Vegas and the families of the victims of this attack," she said. "May it be a comfort to the loved ones of those killed that all of America mourns with them."