Christian Pastor Saeed Abedini, a U.S. citizen sentenced to eight years in an Iranian prison, has spoken out about his plight, which includes physical violence, psychological abuse and death threats.

"This new letter from Pastor Saeed could not be more clear or direct – he continues to face life-threatening abuse simply because of his religious beliefs," said Jordan Sekulow, executive director of the American Center for Law and Justice, which represents the pastor's wife and children in the U.S.

"The letter also underscores the need to move quickly. A U.S. citizen is in failing health from beatings and abuse – a menacing scenario that should command the full attention and engagement of the U.S. government."

In a Feb. 18 letter, the pastor said the conditions in his prison are "difficult." He explained that he is the target of physical violence and acts intended to humiliate him.

In addition, he said that his eyes have become blurry and his steps have become "very weak and shaky."

The pastor said he is "carefully watched" because of his Christian faith, even being attacked by his cellmate to stop him from singing worship songs.

In response, he said, "I hugged him and showed him love. He was shocked."

A native of Iran, Pastor Abedini has been a United States citizen since his 2010 marriage to his American wife.

The pastor is serving an eight year prison sentence for his work with house churches in the country numerous years ago. While these churches are legal, Iran alleges his work threatened national security by attempting to persuade Iranian youth away from Islam.

The pastor, who converted to Christianity from Islam 13 years ago, had worked with house churches until attracting the ire of Iran. In 2009, he came to an agreement with the regime to stop his work with the house churches and turned instead to non-religious orphanages.

He was in the country to work with these orphanages when he was arrested last September. He is now imprisoned in Tehran's Evin Prison, which has a reputation for severity.

The pastor said those in the jail are trying to put him under "sometimes unbearable" pressures "so that they can show me that my faith is empty and not real."

He said they want him to deny Christ.

"But they will never get this from me," he said. "This is why the Bible is Truth and they are in the way of destruction."

Pastor Abedini's wife, Naghmeh, who lives in Idaho with their two children, said it is "heart wrenching" to hear of her husband's continued abuse.

"Now our worst fears have been confirmed. He continues to face life-threatening abuse at the hands of the Iranian officials simply because of his faith in Jesus," she said.

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Naghmeh voiced concern for her husband's health and well-being.

"His situation is dire and with the continued abuse and death threats, we are not sure how long Saeed will survive these horrendous conditions in prison."

The American Center for Law and Justice and its European affiliate filed a statement last week with the U.N. Human Rights Council calling on Iran to release the pastor. It charged that Iran has violated international law and human rights abuses.

In addition, more than 80 members of Congress from both parties sent a letter to U.S. Secretary of State John Kerry last week asking him to "exhaust every possible option" to secure the pastor's immediate release.

Sekulow voiced hope that Kerry will act to help the pastor and highlighted the importance of continued international attention.

In spite of the abuse, Pastor Abedini said he sees these difficulties as "golden opportunities and great doors" to serve God.

"There are empty containers who are thirsty for a taste of the Living Water and we can quench their thirst by giving them Jesus Christ," he said. "Maybe you are also in such a situation, so pray and seek God that He would use you and direct you in the pressures and difficulties of your lives."

"Stay strong for His glory," the pastor urged Christians.