The sister of the last American hostage being held by the Taliban made a desperate plea this week to President Joe Biden as the U.S. military completes its withdrawal from Afghanistan, telling ABC News in an exclusive interview, “I don’t think anybody can come home with their head held high until every stone has been turned.”

U.S. Navy veteran Mark Frerichs, 58, was abducted in Kabul in January 2020 after being lured to what he thought was a new business meeting — but which turned out to be a horrific ruse, family members and officials have said.

Frerichs’ sister, Charlene Cakora, said in an emotional interview that “it is almost too late now” to hope for either a negotiation or hostage rescue mission to secure her brother’s freedom from his Taliban captors, given the military’s hasty move to exit Afghanistan by July Fourth.

But she urged the commander-in-chief to pull out all the stops.

“President Biden,” she addressed the president during the ABC News interview at her home outside Chicago, “oh, please do everything you can to bring my brother home.”

“You have the power to bring my brother home, please get my brother home safely. We are relying on you,” Cakora pleaded, her voice cracking with emotion as she dabbed at tears on her cheeks. “He’s a good man. He deserves better. He does not deserve to be left behind. He’s an American citizen. And I know that you would not leave an American citizen behind, so please, I beg you, do everything you can to get my brother home.”

Cakora has not been given the opportunity to speak directly with either the former or current president.

Asked on Friday about Frerichs’ family’s concerns that their loved one will be left behind, the White House — without specifically naming Mark Frerichs — said they are working to free Americans in captivity.

“The president’s message is that he will continue to fight every day of his presidency to bring Americans home who are detained overseas, whether it’s in Afghanistan or any other country around the world,” said White House Press Secretary Jen Psaki. “Again, we will have a diplomatic presence on the ground. We will continue to work closely with the government, with security support, humanitarian support, and there needs to be continued, a continued political process, ongoing negotiations.”

As the U.S. military completes its withdrawal from Afghanistan after two decades of warfare following the 9/11 attacks, Cakora said she and her husband Chris feel like “our leverage is pretty much gone right now.”

Each week has brought the closing of another American base — Jalalabad and Kandahar, and this week Bagram Airfield — as the Taliban have waged an offensive against government forces, capturing dozens of districts countrywide.

“We can’t lose hope and we have to be strong for Mark, but it’s hard,” said Cakora, who said she’s been passing the time in her garden.

“I do a lot of weed pulling and I take all the frustration out with that,” she said. “And I try not to watch the news too much, as far as that. But it’s been really tough the past month due to the fact that our troops are coming home.”

U.S. officials and sources close to Frerichs’ family confirm that he is being held by a faction of the Taliban, the Haqqani network, known for abducting and holding Westerners captive inside Pakistan’s tribal areas. American diplomats have focused in recent weeks on engaging the government of Pakistan, whose intelligence services have a decades-long relationship with the Haqqani network.

In a statement to ABC News last week, the Pakistani government said there is “no evidence” that Frerichs is being held captive in their country, but pledged to assist in efforts to return him to his family.

Frerichs’ family, frustrated by the lack of progress, say they’re aggravated that it took almost a year and a half for U.S. officials to turn to Pakistan for help.

“They’re not using right methods,” Cakora said. “There’s capabilities, there are stones unturned I firmly believe, and I don’t think anybody can come home with their head held high until every stone has been turned.”

U.S. Special Envoy Zalmay Khalilzad cut an initial armistice deal with Taliban leadership in Doha, Qatar, last year — a month after Frerichs was kidnapped — but Khalilzad did not mention Frerichs publicly for several more months.

Cakora told ABC News that last fall, Taliban leaders in Doha said they were holding Frerichs hostage and had provided him with medical treatment — a startling admission she said Khalilzad shared with her.

“He [Khalilzad] said that he is healthy and well,” Cakora said of her brother. “And that’s pretty much it — he’s healthy and well and he has had some high blood pressure issues, and so he’s seeing the doctor for that, he’s taken medication for that.”

As ABC News has previously reported, Khalilzad has insisted in recent months that he has raised Frerichs’ captivity directly with his counterpart in Doha, Mullah Abdul Ghani Baradar. He has not disclosed what response he has received, but sources say the Taliban chief has not denied that the group’s Haqqani faction has held the American.

“In my meetings with the Taliban, I have demanded his release,” Khalilzad told the House Foreign Affairs Committee on May 18.

It remains unclear why the Taliban kidnapped and continue to hold Frerichs. In the past, hostages such as American Caitlan Coleman and U.S. Army Sgt. Bowe Bergdahl were used as political bargaining chips for the Taliban to demand prisoner releases.

No Taliban were released in exchange for Coleman, who was freed with her three children in 2017 after pressure was put on Pakistan by the Trump administration. Bergdahl, however, was traded for five Taliban who were being held at the Guantanamo prison, in a controversial decision by President Barack Obama.

Taliban negotiators in Doha have been seeking the release from a U.S. federal penitentiary of convicted heroin trafficker Hajji Bashir Noorzai, who was an early bankroller of the extremist group — but the Taliban has never specifically promised Frerichs’ freedom in exchange for Noorzai.

U.S. Department of Justice officials under the Obama, Trump and Biden presidencies have resisted freeing Noorzai from his two life sentences, officials have told ABC News.

Cakora is imploring all involved to free a man who has had no involvement in the “forever war.”

“I just want to tell anybody, the people who are holding Mark, I just want to let you know that Mark’s my brother and I want him home safe,” she said. “And wouldn’t you want your brother home if you were in the same situation?”

Barring the mercy of the Taliban, Cakora said that Biden should do whatever it takes to get the former Navy diver back to his hometown of Lombard, Illinois.

“I think I feel that if they leave a man behind that served this country for six years, I would think that, how could they sleep at night, you know? I mean, how are they sleeping at night knowing that they left a U.S. citizen behind — a U.S. veteran?” Cakora said. “They’re pretty cold if they’re not doing their job, because that’s their job.”