Over 100 members of the European parliament have signed off on a letter to Turkish President Recep Erdogan demanding the release of imprisoned U.S. Pastor Andrew Brunson.

Brunson has been held in a Turkish prison without a trial for 21 months. The letter is the latest in a series of international humanitarian efforts to win his release from jail.

The letter protests the fact that Rev. Brunson had to wait 18 months just to receive an indictment specifying the charges against him. As Newsmax has reported, Brunson’s indictment relies on hearsay evidence from secret witnesses, a practice that would never be allowed by a court in the West. The indictment also appears to equate "Christianization" with terrorism.

Brunson, 50, was arrested in October 2016, He has been charged with "committing crimes on behalf of terror groups without being a member" and "seeking to overthrow the Turkish government.” But the charges are so flimsy, critics note, that the Turkish court case recently refused to let witnesses for the defense.

His real crime, many observers say, was being an American Christian in Turkey when Erdogan initiated a brutal political crackdown after a failed, military coup attempt in July 2016.

Erdogan trying to pressure the U.S. government to hand over Fethullah Gulen, an Islamist cleric refuge in Pennsylvania he blames for inspiring the ill-fated rebellion.

"Give us the pastor back,’ they say," Erdogan remarked in a September 2017 speech. "You have one pastor as well. Give him [Gulen] to us. Then we will try him [Brunson] and give him to you."

The letter from European leaders refers to Brunson as "an innocent political prisoner."

It expresses the signatories’ "deep concern about the wrongful imprisonment of Pastor Andrew Brunson."

If convicted, Brunson could face a sentence of 35 years in Turkey’s notoriously brutal prison system.

The U.S. dignitaries calling for Brunson’s release include President Donald Trump, Vice President Mike Pence, and Secretary of State Mike Pompeo.

In April, a bipartisan group of 66 U.S. senators fired off a letter to Erdogan calling the indictment "an absurd collection of anonymous accusations, flights of fantasy, and random character assassination."

So far there’s little evidence Erdogan faces any domestic political pressure to free Brunson. Turkey is 99.8 percent Muslim, with a tiny population of Christians and Jews.

The international pressure on Erdogan continues to mount, however. A petition calling for Brunson’s release circulated by the American Center for Law and Justice has garnered over 570,000 signatures.

A June report by the Foundation for Defense of Democracies, authored by Aykan Erdemir and Eric S. Edelman, reported that 30 Western nationals were jailed in Turkey following the attempted coup. Nine of them, including Brunson, continue to languish in jail. The report charges that Turkey is conducting what it calls "hostage diplomacy."

Erdemir is a former Turkish parliamentarian, and a global advocate for religious freedom. Edelman is the former U.S. ambassador to Turkey.

Brunson has spent much of his incarceration in solitary confinement, and has reportedly lost over 50 pounds due to illness and stress.

The report concludes, "Only a concerted transatlantic strategy can put an end to Erdogan’s hostage diplomacy, free Western nationals wrongfully detained in Turkey, and prevent American and European citizens from becoming bargaining chips. Without resolute action from its allies, Ankara’s drift from transatlantic values is sure to continue."