National Security Council coordinator John Kirby says Russia has not responded to the "substantial proposal" the U.S. offered back in July regarding the release of WNBA star Brittney Griner and former U.S. Marine Paul Whelan. 

Kirby told the media during Friday’s White House press briefing that the U.S. has made a "serious offer" to negotiate the return of Griner and Whelan, but added that those discussions are "still ongoing."

"They have not responded to our offer. We have made a serious offer to get Brittney Griner and Paul Whalen back home," he said. "The Russians have not responded to that offer. But that doesn't mean that we're not still in negotiations."

BRITTNEY GRINER, PAUL WHELAN’S FAMILIES TO MEET WITH BIDEN AS AMERICANS REMAIN IN RUSSIA JAIL

Kirby was pressed further over the apparent stalemate, but said if he had an answer as to why the Russians haven’t responded, "we might already have a deal." 

"I think that's a better question put to our Russian colleagues. We made a serious offer. We want them to accept it, frankly, these two individuals ought to be home anyway, period. But we understand that that's probably going to have to be the result of the negotiating process, one that we're willing to participate in honestly and fully, and we've been doing that. And we await them to take the offer that's on the table," said Kirby. 

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President Biden was set to meet with the families of Griner and Whelan on Friday. This comes almost two months after Secretary of State Antony Blinken confirmed that the Biden administration made a "substantial proposal" to Russia to facilitate the return of Griner and Whelan.

"What I can tell you for sure is the president is not going to let up," Kirby said Friday. 

"He's confident that this is going to remain at the forefront of his mind and his team's mind. And they're going to continue to work this as hard as they can. We want these two individuals home back where they belong with their families. They should be there already."

Griner was sentenced last month to nine years in prison after pleading guilty to drug charges. She has appealed the decision, while Whelan is serving a 16-year sentence on espionage-related charges that he and his family say are false. 

The Associated Press contributed to this report.