Credit: Charles Dharapak/AP Photo

Friends shouldn't spy on friends, Sen. Susan Collins, R-Maine, told reporters on Tuesday, noting that she is troubled by reports that the National Security Agency was collecting intelligence on U.S. ally leaders.

"The reports are very disturbing. Friends don't spy on friends," Collins said before entering a closed Senate Intelligence Committee meeting on Capitol Hill. "I think that is totally inappropriate. There's absolutely no justification for our country to be collecting intelligence information on the leaders of some of our closest allies."

Collins expressed concern that President Obama didn't know about the program and suggested that if he was unaware, the president should ask for the resignation of those who didn't keep him in the loop.

"If the president didn't know he certainly should have known, and it would be very disturbing if he did not know," Collins said. "I would think that if the president was not informed of this program, that he would be demanding resignations of those who should have informed him."

Sen. Dianne Feinstein, D-Calif., the chairwoman of the Senate Intelligence Committee, declined to respond when asked if the White House has informed her if it will stop surveillance on our allies.

Meanwhile, White House Press Secretary Jay Carney refused to comment on reports that the U.S. is considering halting programs that monitor foreign leaders, reiterating that the administration is continuing to review its surveillance operations around the globe.

"The review is ongoing, so I'm not going to discuss the details or the outcomes … until it's completed. But as I said, we've made some decisions, the president has made some decisions, and I would expect that we'll make more as this process continues. And then when it's over, we'll have more to say about the decisions we've made," he said.

"Is the United States now listening in on the phone conversations of friendly presidents and prime ministers?" ABC News' Jonathan Karl asked.

"I'm not going to get into discussion of specific reported activities, intelligence-gathering activities," Carney said.