A U.S. surveillance court has given the National Security Agency no limit on the number of U.S. telephone records it collects in the name of fighting terrorism, the NSA director said Thursday.

The NSA intends to collect all U.S. telephone records and put them in a searchable “lock box” in the interest of national security, General Keith Alexander, the NSA’s director, told U.S. senators.

“There is no upper limit” on NSA telephone-records collection, Alexander said. “I believe it is in the nation’s best interest to put all the phone records into a lock box that we can search when the nation needs to do it.”

The NSA would need to notify the U.S. Foreign Intelligence Surveillance Court and Congress before collecting some other types of U.S. communications, including mobile-phone location information, Alexander told senators. The NSA doesn't currently have plans to collect mobile-phone location information, he said.

Alexander, other intelligence officials and several members of the Senate Select Committee on Intelligence defended the NSA’s data collection and surveillance efforts during a committee hearing.

The NSA collection of U.S. phone records, disclosed by former NSA contractor Edward Snowden earlier this year, are “lawful, effective and constitutional,” said Senator Dianne Feinstein, a California Democrat and chairwoman of the committee.

Nevertheless, Feinstein said she's working on a bill that would add transparency to the data collection process at the NSA and the surveillance court. Some of the provisions she described would reinforce current NSA practices, but the bill would also give the NSA new authority to continue to conduct surveillance on foreign suspects who enter the U.S. while the agency seeks court-ordered warrants.

Feinstein, chairwoman of the committee that's supposed to oversee the NSA surveillance programs, at one point interrupted witness Tim Edgar, a former director of privacy and civil liberties for the White House, when he talked about the NSA's unauthorized collection of some U.S. communications. Feinstein defended the NSA, saying the agency immediately reported the mistake to the surveillance court.

"I really believe the NSA is extraordinarily careful in what they do," she said. "I have great faith in the NSA."

NSA mistrust?

Alexander, Director of National Intelligence James Clapper, and some committee members blamed what they called inaccurate media reports on the Snowden leaks for creating an environment of mistrust in the NSA by the general public.

Some media organizations are feeding “raw meat to people who refuse to look at the facts” that the NSA’s data collections are legal and protect privacy, said Senator Dan Coats, an Indiana Republican.

“It’s very frustrating to know that we have programs that comply with the law, that have been approved by the Congress, that have been approved by the president of the United States, that are saving Americans’ lives, and there are efforts to compromise those programs to convince a nontrusting public,” Coats said. “Had we not had these programs in place, I’d hate to think of what we’d be talking about” at the hearing.

Clapper agreed with Coats. Intelligence officials are frustrated in their efforts to “counter the popular narrative” about the surveillance programs, he said.

But Senator Ron Wyden, an Oregon Democrat and critic of the NSA programs, pointed his finger back at U.S. intelligence officials. Abuses alleged in the NSA programs were bound to be made public, said Wyden, who introduced legislation Wednesday that would prohibit bulk collection of phone records by the NSA.

“I believe that any government official who thought that the intrusive, constitutionally flawed surveillance system would never be disclosed was ignoring history,” Wyden said. “The leadership of your agencies built an intelligence collection system that repeatedly deceived the American people. Time and time again, the American people were told one thing about domestic surveillance in public forums, while government agencies did something else in private.”

Updated at 3:25 p.m. PT with additional information about mobile-phone location data collection.