Britain's Queen Elizabeth has sent "thoughts and prayers" to those affected by the mass shooting in Orlando.
Queen Elizabeth
At least 50 people died and 53 were injured when a gunman opened fire inside gay nightclub Pulse on Sunday (12.06.16) morning and the monarch - who celebrated her official 90th birthday over the weekend - has issued a message of support to the US.
A statement issued through Buckingham Palace's Twitter page said: "Prince Philip and I have been shocked by the events in Orlando. Our thoughts and prayers are with all those who have been affected."
US President Barack Obama condemned the shooting as an "act of terror" and vowed to do whatever he could to help those in Orlando.
He said in a statement: "Today, as Americans, we grieve the brutal murder -- a horrific massacre -- of dozens of innocent people. We pray for their families, who are grasping for answers with broken hearts.
"We stand with the people of Orlando, who have endured a terrible attack on their city. Although it's still early in the investigation, we know enough to say that this was an act of terror and an act of hate.
"And as Americans, we are united in grief, in outrage, and in resolve to defend our people...
"This morning I spoke with my good friend, Orlando Mayor Buddy Dyer, and I conveyed the condolences of the entire American people. This could have been any one of our communities. So I told Mayor Dyer that whatever help he and the people of Orlando need -- they are going to get it. As a country, we will be there for the people of Orlando today, tomorrow and for all the days to come."
Meanwhile, Pope Francis reacted in "horror" and "condemnation" after hearing about the tragedy.
A statement from the Vatican press office said: "We all hope that ways may be found, as soon as possible, to effectively identify and contrast the causes of such terrible and absurd violence which so deeply upsets the desire for peace of the American people and of the whole of humanity."
British Prime Minister David Cameron was "horrified" by the news.
He tweeted: "I'm horrified by reports of the overnight shooting in Orlando. My thoughts are with the victims and their families."
Omar Mateen has been named as the killer and was shot down by police.
He has reportedly been linked with extremist group ISIS, but Pakistan's Prime Minister Nawaz Sharif insisted the shooting didn't "represent the will of a vast majority of Muslims."
He added: "It is just another representation of a cancer of radicalisation -- one that we promise to fight every day of our lives."
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