Orlando gay nightclub shooting 'an act of terror and hate
Americans were united in "grief, outrage and resolve to defend our people", he said.
Omar Mateen, 29, killed 50 people and wounded 53 at the Pulse club before being shot dead by police.
The so-called Islamic State group has said it was behind the attack, but the extent of its involvement is not clear.
A statement on its affiliated Amaq news agency said that an IS "fighter" was responsible.
NBC News reported that Mateen had called the emergency services before the attack and swore allegiance to IS.
The gunman was killed in an exchange of fire with 11 police officers, after taking hostages at the club.
The attack is the worst mass shooting in recent US history.
Eight of the victims have so far been named: Edward Sotomayor Jr, Stanley Almodovar III, Luis Omar Ocasio-Capo, Juan Ramon Guerrero, Eric Ivan Ortiz-Rivera, Peter O Gonzalez-Cruz, Luis S Vielma and Kimberly Morris.
A moment of silence was observed across the US at 18:00 local time (22:00 GMT).
In an apparently unrelated event, a heavily armed man was held on weapons and explosive materials charges in southern California after saying he wanted to go to a gay pride event in Los Angeles.
Read more at BBC
