The US officials, quoted by the Washington Post, said the safe house was the base for intelligence gathering that began after Bin Laden's compound was discovered last August, and which was so exhaustive the CIA asked Congress to reallocate tens of millions of dollars to fund it.
"The CIA's job was to find and fix," the Post quoted one US official as saying, using special forces terminology for locating a target. "The intelligence work was as complete as it was going to be, and it was the military's turn to finish the target."
US officials told the New York Times that intelligence gathered from computer files and documents seized at his compound showed Bin Laden had for years orchestrated Al-Qaeda attacks from the Pakistani town.
One US official said there was no indication from the intelligence that further plans were drawn up for the railway plot or that steps were taken to carry it out. The US Department of Homeland Security said it had no information of an imminent threat.
The CIA spent several months monitoring Bin Laden's hideout, watching and photographing residents and visitors from a rented house nearby, according to US officials quoted in the New York Times and Washington Post.
Observing from behind mirrored glass, CIA officers used cameras with telephoto lenses and infrared imaging equipment to study the compound, and they used sensitive eavesdropping equipment to try to pick up voices from inside the house and to intercept cell phone calls, the New York Times said. A satellite used radar to search for possible escape tunnels.
The US administration has refused to be drawn on details on the raid, but, in a further sign of fractious relations between the allies, senior Pakistani security officials told Reuters that US accounts had been misleading.
In Washington, people familiar with the latest US government reporting on the raid told Reuters on Thursday that only one of four principal targets shot to death by US commandos was involved in any hostile fire.
As the elite Navy SEALs moved in on a guest house inside Bin Laden's compound, they were met with fire and shot a man in the guest house. He proved to be Abu Ahmed al-Kuwaiti, an al Qaeda courier US intelligence agencies had long been tracking.
The commandos then entered the main residence, where they killed another courier and a son of Bin Laden, the sources said. They finally shot and killed the Al-Qaeda leader in a top-floor room after having earlier fired at him as he poked his head out of a door or over a balcony.
US officials originally spoke of a 40-minute firefight. The White House has blamed the "fog of war" for the changing accounts.
