The Texas man arrested on Friday for charging at the White House was armed with a knife when he climbed a fence and made it into the executive mansion after President Barack Obama had departed, the US attorney's office said on Saturday.
Previously, the US Secret Service had said Omar Gonzalez, 42, had been unarmed.
Gonzalez was charged with unlawfully entering a restricted building or grounds while carrying a "deadly or dangerous weapon," according to an affidavit released by the US attorney's office on Saturday.
If convicted, he faces up to 10 years in prison.
The affidavit, signed by Daniel Hochman, a Secret Service officer on duty at the White House when the incident occurred, said Gonzalez was carrying a folding knife with a 3-1/2-inch long serrated blade.
It said Gonzalez went through the north doors and got inside the mansion.
"After he was apprehended, Omar Gonzalez told United States Secret Service Agent Lee Smart that he was concerned that the atmosphere was collapsing and (he) needed to get the information to the President of the United States so that he could get the word out to the people," the affidavit said.
The incident, one of the most significant breaches since Obama became president, raised questions about security procedures at the White House, a heavily guarded complex filled with Secret Service officers and snipers.
The Secret Service increased security around the White House on Friday and started a review of its response, including a physical assessment of the area and interviews with involved personnel, the agency said.
Shortly before the intrusion, Obama and his daughters had departed for Camp David. First Lady Michelle Obama had traveled separately to the presidential retreat in nearby Maryland.
"Every day the Secret Service is challenged to ensure security at the White House complex while still allowing public accessibility to a national historical site," the agency said in a statement.
"Although last night the officers showed tremendous restraint and discipline in dealing with this subject, the location of Gonzalez's arrest is not acceptable."
The results of the review will be delivered to Homeland Security Secretary Jeh Johnson.
While waiting for the results of the review, Secret Service Director Julia Pierson ordered increased security around the area where the intruder got onto the White House grounds.
Tourists and others can get a close-up view of the front of the mansion from Pennsylvania Avenue, which is closed to traffic but open to pedestrians and runs directly in front of the complex.
"Director Pierson has ordered the immediate enhancement of officer patrols and surveillance capabilities along the Pennsylvania Avenue fence line around the White House complex," the statement said.
"These measures went into effect last night," it added.
An Obama spokesman said the president had full faith in the agency charged with protecting him and was certain the review would be conducted thoroughly and professionally.
"The president has full confidence in the Secret Service and is grateful to the men and women who day in and day out protect himself, his family and the White House," spokesman Frank Benenati said.
A second man was arrested on Saturday for trespassing at the White House. Secret Service spokesman Ed Donovan said the man approached the White House gates on foot, was sent away, then returned in his vehicle.
"He refused to leave and was arrested for trespassing," Donovan said. No further details were available.
The Secret Service has faced a series of scandals and other security breaches in recent years. In 2009 an uninvited couple penetrated layers of security to get into a White House state dinner. The agency's reputation was tarnished further in 2012 over a prostitution scandal involving its agents in Colombia.