The young Muslim men, who are from the Washington D.C. area, were captured in the eastern Pakistan city of Sargodha in a case that has spurred fears that Westerners are traveling to Pakistan to join militant groups.
Tahir Gujar, a senior police investigator in Sargodha, said police had almost concluded their investigation and that the men would appear in an anti-terrorist court in the city on Jan. 4.
"We are certain that these five Americans wanted to carry out attacks in Pakistan, and we will seek life imprisonment for them," he said.
Under Pakistan's complicated judicial system, the police will recommend the charges during the court appearance on Monday. However, the court might not charge the men immediately, and the five will likely be given time to prepare their defense after they have seen the charges.
Gujar didn't say what police believe the men intended to target.
Authorities have said that the five had a map of Chashma Barrage, a complex that includes a water reservoir and other structures in the populous province of Punjab. It is located near nuclear power facilities about 200 kilometers (125 miles) southwest of the capital, Islamabad.
Pakistan has a nuclear weapons arsenal, but it also has nuclear power plants for civilian purposes.
Any nuclear activity in Pakistan tends to come under scrutiny because of growing Islamic militancy and the South Asian nation's past history of leaking sensitive nuclear technology due to the actions of the main architect of its atomic weapons program, Abdul Qadeer Khan. But as militancy has spread in Pakistan, officials have repeatedly insisted the nuclear weapons program is safe.
Pakistani police and government officials have made a series of escalating and, at times, seemingly contradictory allegations about the five men's intentions, while U.S. officials have been far more cautious, though they, too, are looking at charging the men.
Officials in both countries have said they expected the men would eventually be deported back to the United States, but charging the men in Pakistan could delay that process. Pakistan's legal system can be slow and opaque.
In an interview with The Associated Press last week, Punjab province Law Minister Rana Sanaullah said the men had established contact with Taliban commanders. He said they had planned to meet Pakistani Taliban chief Hakimullah Mehsud and his deputy Qari Hussain in Pakistan's tribal regions before going on to attack sites inside Pakistan.
The nuclear power plant "might have been" one of the targets, Sanaullah alleged.
The U.S. Embassy declined to comment on the potential charges and would not say what efforts Washington was making to bring the men back.