The Justice Department's seizure of phone records for journalists at the Associated Press (AP) is hurting the agency's ability to gather news, the wire service's Chief Executive and President Gary Pruitt said on Sunday.

"Officials that would normally talk to us and people we talk to in the normal course of news gathering are already saying to us that they're a little reluctant to talk to us," Pruitt said on CBS's Face The Nation program.

"They fear that they will be monitored by the government."

The Justice Department told the AP on May 10 that it had earlier seized records of more than 20 of its phone lines for April and May 2012. The seizure was part of an investigation of media leaks about a foiled terrorism plot.

"Approximately a hundred journalists use these telephone lines as part of news gathering," Pruitt said.

"And over the course of the two months of the records that they swept up, thousands upon thousands of news-gathering calls were made."

The White House has said that President Barack Obama learned about the Justice Department's record seizure from press reports and had no prior knowledge of the action.

Pruitt said the Justice Department claimed an exception to its own rules that required them to notify the AP of such a record seizure by saying that such a disclosure would have posed a substantial threat to the investigation.

"But they have not explained why it would and we can't understand why it would," Pruitt said.

Officials have told Reuters that the AP phone records were just one element in an ongoing sweeping US government investigation into media leaks about a Yemen-based plot to bomb a US airliner, prompted by a May 7, 2012 AP story about the operation to foil the plot.

Pruitt said the AP would have sought to narrow the scope of the record seizure through courts had it been notified, instead of "the Justice Department acting on its own, being the judge, jury and executioner, in secret."