As President Donald Trump prepares for a historic meeting with North Korean leader Kim Jong Un, religious freedom advocates are urging the U.S. president to negotiate the release of the remaining prisoners in North Korea’s labor camps.

On May 17, more than 50 scholars, religious leaders, and human rights advocates sent a letter to President Trump and key foreign policy leaders requesting that the U.S. incorporate human rights in the nuclear negotiations set for June 10 in Singapore.

While acknowledging that the successful denuclearization of North Korea would “benefit all of humanity,” the letter recommends specific terms that could be added to a negotiated agreement to assist those suffering from North Korea’s human rights abuses.

“We also implore you to recognize that there are tens of thousands of other men, women, and even children -- most of them North Korean citizens and many of them Christians -- being brutalized by Kim and his regime,” reads the letter written by the Religious Freedom Institute.

Archbishop William Lori of Baltimore, chair of the U.S. bishops’ religious freedom committee, was among the letter’s signatories, alongside a number of Catholic scholars, including Princeton Professor Robert George and former U.S. Ambassador to the Holy See Miguel Diaz.

Elliot Abrams, senior fellow at the Council on Foreign Relations; Nicholas Eberstadt, a founding director of the Committee for Human Rights in North Korea; Winston Lord, former U.S. Ambassador to China; and Greg Mitchell, co-chair of International Religious Freedom Roundtable, were also among the signatories.

The letter recommends four particular requests that President Trump should negotiate with Kim Jong Un. These include allowing the International Red Cross access to all of North Korea’s prisons within one month of any signed agreement and “the immediate release of substantial numbers of prisoners of conscience.”

There are currently an estimated 80,000 to 120,000 people in North Korea’s six political prison camps, in which the U.S. State Department has found evidence of starvation, forced labor, and torture.

These prison camps have been documented by Google Earth satellite imagery, and detailed in the biographies of North Korean defectors were formerly imprisoned, such as Shin Dong-Hyuk’s “Escape from Camp 14” and Kang Chol-Hwan’s “The Aquariums of Pyongyang.”

Photographs of suffering North Korean citizens, as well as the United Nations human rights commission report on North Korea and other documents are attached to the letter to President Trump.

The 400-page United Nations report found that the gravity, scale and nature of the “unspeakable atrocities” committed by the North Korean regime “reveal a State that does not have any parallel in the contemporary world.”

“These crimes against humanity entail extermination, murder, enslavement, torture, imprisonment, rape, forced abortions and other sexual violence, persecution on political, religious, racial and gender grounds, the forcible transfer of populations, the enforced disappearance of persons and the inhumane act of knowingly causing prolonged starvation,” according to the UN report published in 2014.

Vice President Mike Pence, Secretary of State Mike Pompeo, National Security Advisor John Bolton and others were also sent copies of the letter.

Earlier this month, Secretary Pompeo traveled to North Korea, bringing home with him three Americans who had been imprisoned in North Korea. According to the White House, the prisoners’ release by North Korea was a gesture of goodwill ahead of the summit.

In recent days, North Korea has threatened to cancel the highly anticipated summit between President Trump and Kim Jong Un in objection to the continuation of U.S.-South Korean military exercises.

However, White House Press Secretary Sarah Sanders told reporters on May 16 that this threat from North Korea to cancel the talks was “fully expected” and that the White House is hopeful that the summit will still take place.