National Security Adviser John Bolton did not dismiss outright the idea of using private contractors to help fight the U.S. war in Afghanistan, telling ABC News' This Week on Sunday that he is "always open to new ideas."

The idea, touted by Blackwater founder Erik Prince, has gained steam amid frustration with the progress of the Afghanistan war, the longest continuous operation in American history.

Some congressmen fear that President Donald Trump will back Prince's idea, resulting in pulling troops out, while others are concerned about the ethics of using government contractors to engage in war, as well as its perceived harm to national security.

But when asked about the idea on ABC, Bolton responded that, there's always a lot of discussions. I'm always open to new ideas, but I'm not going to comment on what the thinking is. That will ultimately be the president's decision.

Bolton added that the administration has "looked at several different possibilities to get the Taliban and others directly engaged with the government of Afghanistan. There have been some signs that's moving in the right direction."

I don't rule out that we'd have a change in some of the things we're doing there, but the president's view is that he'll support the government of Afghanistan in its efforts to see if the Taliban are finally ready to talk seriously, Bolton said.

A spokesperson for the National Security Council told CBS News, "no such proposal from Erik Prince is under consideration.

The NSC spokesperson emphasized that, the president adopted the South Asia strategy after months of deliberation among his key national security advisors," adding that Trump, "like most Americans, would like to see more progress in Afghanistan. However, he also recognizes that withdrawing precipitously from Afghanistan would lead to the re-emergence of terrorist safe havens, putting American national security and lives in danger."