(CNN) The White House and Capitol Hill are considering a phone app connected to the National Instant Criminal Background Checks (NICS) as one of the options in their discussions for plans to reduce gun violence, according to a Senate source and a person familiar with the talks.

The proposed app would be used for background checks using private sales, and not for purchases involving commercial dealers, one of the sources told CNN. The Washington Post first reported on the app.

White House aides have spent the last month meeting with congressional staffers and devising a package of legislative measures in the wake of recent mass shootings . The Department of Justice also prepared a package of options that was delivered to the White House more than two weeks ago.

On Thursday, senior advisers presented President Donald Trump with summaries of the various courses of action on gun violence.

During the briefing, officials did not delve into legislative details and Trump did not appear interested in some of the nitty-gritty of how each proposal would work, the person familiar said.

Separately, the source told CNN the lack of clarify is leading to doubts Trump will back a bipartisan measure on expanded background checks from Democratic Sen. Joe Manchin of West Virginia and Republican Sen. Pat Toomey of Pennsylvania, or some modified version of it.

Trump initially appeared open to expanding background checks following two mass shootings in El Paso, Texas, and Dayton, Ohio, last month, but backed off after pressure from the National Rifle Association.

During high-level calls between the Justice Department and Capitol Hill Friday night, Attorney General Bill Barr sent a signal that talks have come to a grinding halt, and prospects for presidential support for expanding background checks appear to be dimming as the week draws to a close, an official familiar with the conversations told CNN.

According to the official, Michael Williams, a deputy to the President who used to work for the NRA, has killed or delayed any progress on such a bill, despite support from Barr and the President's daughter and White House adviser Ivanka Trump.

Officials still expect a plan to be released next week.

Currently, there are no federally mandated background checks for private sales.

"This proposal reveals one important fact from the White House: they recognize the problem of the private sale loophole that allows 20 percent of guns to be sold with no background check at all. ... We agree the private sale loophole must be fixed, but it should be fixed in a way that allows meaningful enforcement, not easy circumvention that endangers lives," said Kris Brown, president of Brady, a gun violence prevention advocacy group. "The right balance was struck by the House, which passed a background checks bill where sales by private sellers are completed by a federally licensed firearms dealer to confirm the person purchasing the gun is the same person who is picking up the gun and other assessments of risk before completion of the sale are done. If we want to save lives and meaningfully fix the private sale loophole, S. 42, now 200 days and counting on Mitch McConnell's desk is the way to do it."

Gun rights and privacy advocates have already voiced concerns about an app like the one proposed, saying it could become a de-facto registry and worry about how secure the information would be.

Here are some of the options being proposed in discussions, in addition to measures Trump and his aides have floated publicly: