The Pakistani-American suspect arrested on suspicion of trying to detonate a car bomb in New York's Times Square told investigators he acted alone and denied any ties to radical groups in his native Pakistan, a U.S. law enforcement official familiar with the investigation said on Tuesday.

"He's admitted to buying the truck, putting the devices together, putting them in the truck, leaving the truck there and leaving the scene," the source told Reuters, speaking on condition of anonymity.

"He's claimed to have acted alone. He did admit to all the charges, so to speak," the source said, adding that investigators were still looking into his activities during a recent trip to Pakistan.

Faisal Shahzad, 30, was arrested late on Monday on suspicion he bought the sport utility vehicle used to carry a crude bomb made of fuel and fireworks into Times Square last Saturday evening. Had the bomb detonated, many people could have died, officials said.

Shahzad, who received U.S. citizenship last year, was arrested at New York's John F. Kennedy airport while trying to fly to Dubai, officials said.

Shahzad recently visited Pakistan for about five months, returning to the United States in February, the source said.

"Based on our collective experience it's hard to really believe that this is something someone would do on their own. It seems hard to pull off alone. There's a lot we don't know yet," the source said.

Shahzad was due to appear before a U.S. judge later on Tuesday.