Ahmad Khan Rahami's father said he reported concerns about his son being involved with militants to the FBI two years ago
Federal prosecutors on Tuesday charged the suspect arrested after weekend bombings in New York and New Jersey with four counts including use of weapons of mass destruction and bombing a place of public use.
His father said he reported him to the authorities two years ago.
The charges were laid out in a federal complaint that said a handwritten journal was found on the suspect, Ahmad Khan Rahami, that praised Osama bin Laden, the mastermind of the 11 September 2001 attacks and accused the US government of slaughtering Islamist fighters in Afghanistan, Iraq, Syria and Palestine.
The federal charges come after the father of Rahami, who was captured on Monday in New Jersey after a shootout with police, said he had reported concerns about his son being involved with militants to the Federal Bureau of Investigations two years ago.
The FBI acknowledged it had investigated Rahami in 2014, but found no "ties to terrorism" and dropped its inquiry.
The White House said on Tuesday it appeared that the bombings were "an act of terrorism" as an investigation continued into whether Rahami had accomplices, or if he picked up militant views during trips to Afghanistan and Pakistan.
"The investigation is active and ongoing, and it is being investigated as an act of terror," US Attorney General Loretta Lynch said in Lexington, Kentucky.
Rahami, 28, was suspected in the weekend bombings, including a blast on Saturday night in New York City's Chelsea neighbourhood that wounded 29 people, and another on the New Jersey shore that injured no one earlier that day.
Rahami was arrested on Monday in Linden, New Jersey, after a shootout with police that left him with multiple gunshot wounds. He was listed in critical but stable condition, and police had not yet been able to interview him in depth, New York Police Department Commissioner James O'Neill said.
His father, Mohammad Rahami, briefly emerged on Tuesday from the family's restaurant in Elizabeth, New Jersey, telling reporters, "I called the FBI two years ago."
The FBI said in a statement that it began an assessment of the younger Rahami in 2014 based on comments his father made about his son after "a domestic dispute".
One US law enforcement official said the elder Rahami met twice with the FBI, first saying he was worried his son was hanging out with people who might have connections to militants, but two weeks later contending his real concern was that the son was associating with criminals.
Another law enforcement official said the father "recanted the whole story" about his son associating with terrorists.
The comments by the officials, who spoke on the condition of anonymity, showed Rahami had been brought to the attention of the FBI before the bombings much like others who have carried out attacks in the United States in recent years.
For example, the FBI had received tips on both the Orlando nightclub shooter who killed 49 people in June and the lead bomber in the 2013 Boston Marathon attack before they acted.
A neighbour said Rahami had recently started dressing in more traditional clothes such as long tunics and sandals, which she said was how his father dressed.
"I always saw him outside talking on a cell phone, walking back and forth," said the neighbour, who asked not to be identified. "His brother was friendlier, you always saw him with friends. I never saw him with a group of friends."
In a separate incident, a stabbing spree at a Minnesota shopping mall by a Somali-American suspect is being investigated as a potential act of terrorism.
However, investigators have uncovered nothing to tie Dahir Ahmed Adan to organised extremist groups, the local police chief said.
A news agency with ties to the Islamic State (IS) group said the rampage was carried out by an IS "soldier".
Police say Adan stabbed 10 people with a knife at a shopping mall, until an off-duty police officer fatally shot him.