Updated 12:45 p.m. EST

President Obama paid tribute to the victims of today's Colorado shooting tragedy and asked for Americans to pray for the people of the Denver suburb where the movie theater shooting spree happened.

Obama's remarks came in Fort Myers, Fla., where he was scheduled to speak at a campaign event. Obama spoke only briefly and centered his comments on the tragedy.

"There are going to be other days for politics," Obama said. "This is a day for prayer and reflection."

Obama said that after he was briefed about the shooting early Friday morning, he immediately thought of his two daughters, who, like most young people, enjoy going to the movies.

"If there is any takeaway from this, it's that life is fragile," Obama said. "Our time here is limited, and it's precious."

Vice President Biden and first lady Michelle Obama also canceled their events today, said Obama campaign spokeswoman Jen Psaki. The first lady was scheduled to travel to Virginia for two events, and Biden was supposed to appear at a campaign event in Houston.

In a statement, Biden said he knows "what it's like to wait and wonder." Biden lost his first wife, Neilia, and his daughter, Naomi, in a car accident in 1972. His two sons were injured in the crash but survived.

"The reason this is so deeply felt by all Americans is that, but for the grace of God, the victims could have been any one of our children, in any one of our towns," Biden said in a statement. "It is every parent's worst nightmare to receive 'that phone call' and to sit by their child's bedside, praying."

Obama spoke with Colorado Gov. John Hickenlooper and the mayor of Aurora, the Denver suburb where the shooting occurred. After returning to Washington Friday afternoon, he signed a presidential proclamation calling for U.S. flags at the White House and other federal buildings and property to be flown at half-staff in honor of the Colorado victims until sunset Wednesday.

"We do not believe at this point there was an apparent nexus to terrorism," said White House spokesman Jay Carney.

Psaki said Obama campaign officials have asked affiliates in Colorado to pull down all ads for the time being. The Mitt Romney campaign has also pulled advertising in the Colorado market, said Romney spokeswoman Andrea Saul.

"It takes time for stations to be able to do this, but we are making every effort," Psaki said.

The Romney campaign said the likely GOP nominee will address the Colorado incident today at a previously scheduled campaign event. Both Romney and his wife, Ann, have canceled scheduled events.

In a statement earlier today, Obama called the shooting "horrific and tragic" and said his administration stands ready to help the people of Aurora, Colo.

"We are committed to bringing whoever was responsible to justice, ensuring the safety of our people and caring for those who have been wounded," Obama said. "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."

The president was notified of the shooting by his deputy national security adviser for homeland security and counterterrorism, John Brennan, at 5:26 a.m. ET, Carney said. Obama received a follow-up briefing shortly before he spoke from FBI Director Robert Mueller, White House Chief of Staff Jack Lew and Brennan, Carney said.

Obama was in Florida on the second day of a two-day campaign trip.

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Romney called the violence "senseless."

"We are praying for the families and loved ones of the victims during this time of deep shock and immense grief," Romney said in a statement. "We expect that the person responsible for this terrible crime will be quickly brought to justice."

A gunman opened fire early Friday at a suburban Denver movie theater on the opening night of the latest Batman movie The Dark Knight Rises, killing 12 people, the Associated Press reports. A suspect, identified as James Holmes, 24, is in custody.

Obama said the federal government stood ready to assist Aurora in the aftermath of the shooting.

"We're going to stand by our neighbors in Colorado at this extraordinarily difficult time," Obama said. "Even as we learn how this happened and who is responsible, we may never understand what leads anybody to terrorize their fellow human beings like this. Such violence, such evil, is senseless. It's beyond reason. While we will never know fully what causes somebody to take the life of another. We do know what makes life worth living."