President Obama has said he is "shocked and saddened" by the shooting at the Batman film screening in the town of Aurora, Colorado.
In a statement put out on Friday morning, Obama said his administration would "do everything that we can to support the people of Aurora in this extraordinarily difficult time".
"We are committed to bringing whoever was responsible to justice, ensuring the safety of our people, and caring for those who have been wounded.
"As we do when confronted by moments of darkness and challenge, we must now come together as one American family.
"All of us must have the people of Aurora in our thoughts and prayers as they confront the loss of family, friends, and neighbors, and we must stand together with them in the challenging hours and days to come."
Up to 14 people are confirmed dead after a man hurled a tear gas bomb and then opened fire during a midnight Dark Knight Rises film screening in the town near Denver, Colorado.
Witnesses say the man was wearing a "Bane-style" gas mask and body armour during the attack and a bomb squad are reportedly examining a Hyundai in the cinema's car park for a further explosive device.
Obama, who is currently in Florida, was told of the shooting at 5:26am by John Brennan, his assistant for Homeland Security and Counterterrorism.
Mitt Romney, the presumptive Republican nominee for president said he was "deeply saddened by the news of the senseless violence".
"We are praying for the families and loved ones of the victims during this time of deep shock and immense grief."
He added: "We expect that the person responsible for this terrible crime will be quickly brought to justice.”