This message has been sent to U.S. President Donald Trump: Help free a detained pastor in Turkey.

The family of Pastor Andrew Brunson and other religious liberty campaigners are asking President Trump to speak to Turkish President Recep Tayyip Erdogan and push for the release of the North Carolina Presbyterian pastor, ABC 11 reported.

Brunson has been languishing in a Turkish prison for four months now.

An appeal was issued last December for Brunson's release, but the appeal was denied by Turkish authorities, according to Mission Network News (MNN).

Brunson is accused of "membership in an armed terrorist organisation," a charge that his family says has no basis whatsoever.

His family believes that Brunson is being persecuted for his Christian belief.

The American Center for Law and Justice (ACLJ) has created an online petition for Brunson's release. It currently has over 192,700 signatures.

The pastor has spent 23 years building churches and spreading the gospel in Turkey until he applied for residency last October only to be arrested.

Brunson was initially detained together with his wife Norine, who was subsequently released.

Court documents showed that an anonymous source was the basis for Brunson's arrest, according to MNN.

Todd Nettleton with The Voice of the Martyrs, USA said the arrest appears to be a political move. He cited two possibilities. "One is the Islamic leader [Fethullah] Gulen who is in the United States, the Turks have asked the U.S. to extradite him back to Turkey, and the U.S. has said no. It is possible that Andrew Brunson is, in some ways, a pawn in that game to try to encourage the United States to extradite Fethullah Gulen," Nettleton said.

"The other possibility is just that [Brunson] was caught up in the crackdown that is going on across Turkey since the coup attempt last year. The numbers are staggering, more than 40,000 people have been arrested since the coup attempt — political party members, military personnel, journalists, teachers, judges, lawyers," he added.

Brunson's daughter Jacqueline said it's "outrageous to think that this is happening to an American citizen."

ACLJ executive counsel Cece Heil said Brunson's family is now putting their faith in the hands of Trump and other U.S. politicians.

"We are hopeful that President Trump, if he has the chance to speak with President Erdogan, he'll raise this issue with them," Heil said.