The three have been held since soon after the May 1 attempted car bombing, but the announcement marks the first time the authorities here have formally acknowledged their arrest. They had previously been picked up by the country's secretive intelligence agencies.
The three to be charged were identified as Shoaib Mughal, Shahid Hussain and Humbal Akhtar. All three are educated, relatively wealthy Pakistanis.
Complete Coverage: Terrorism in the U.S.
An intelligence officer said an unspecified number of other suspects were still under investigation, but confirmed that two people previously held had been released. He identified one of those as Salman Ashraf, the co-owner of a catering company the U.S. Embassy accused of terrorist ties. The officer spoke on customary condition of anonymity.
Islamabad Police Deputy Inspector General Bin Yamin said Mughal, Hussain and Akhtar would soon be charged in court with terrorism offenses.
He did not give specifics, but terrorism crimes can be punished by death in Pakistan. It was unclear if the men had been appointed lawyers yet. Terrorism trials in Pakistan are always behind closed doors and often last for many months, if not years.
Yamin described them as having "militant minds" and a strong hatred for America.
Pakistani-American has pleaded guilty to terrorism and weapons charges in the United States in connection with the botched bombing.
Yamin said the three suspects had close ties to the leadership of the Pakistani Taliban, a militant group based in the northwest that has claimed responsibility for the plot.
He said the three helped Shahzad to travel to the northwest and meet militant leaders there.
They also sent him $13,000 in the United States when he ran short of money, he said.
Intelligence officers have previously said they had evidence Mughal uploaded video and audio messages from the Pakistan Taliban, including two audio messages from the group's commander, Hakimullah Mehsud, soon after the attack.
An officer has said Mughal was a computer engineer who had a large computer dealership in Islamabad.
Akhtar's wife said soon after his detention that he had graduated from a private university in Islamabad and worked briefly for the government before starting a graphic design business. She said he had no connection to terrorism.
Ashraf's arrest was announced the same evening the U.S. Embassy in Pakistan issued a warning saying that his catering company, Hanif Rajput Catering Service, was suspected of ties to terrorist groups. The firm had previously catered events for the embassy.
"I just say I want to say thank God that my son is back with me with full dignity and honor," said his father, Rana Ashraf Khan, who has long maintained his innocence.
In July, law enforcement officials told CBS News that investigators from the FBI laboratory detonated a replica of the car bomb used in the failed attack to had it actually blown up.
The law enforcement sources said the recreation indicated that the components - including three barbecue grill-size propane tanks, assorted fireworks, nails and tacks - if rigged properly would have severely damaged the SUV carrying the device and the flying flaming debris would have damaged nearby vehicles and property and likely caused injury and possible death to innocent bystanders.