Yusef Naderkhani, a Christian pastor sentenced to death for apostasy may yet be acquitted, his lawyer has claimed.

"I have provided the court with explanations that I believe will make the court change its decision, and it is 90 to 95 percent likely that the court will acquit Naderkhani," Mohammad Ali Dadkhah, Naderkhani’s attorney, said to Radio Farda, the Iranian Branch of Radio Free Europe/Radio Liberty's (RFE/RL) broadcast services.

International outrage has been simmering over Iran’s conviction of the Christian pastor, who converted from Islam to Christianity in 1997, when he was 19. He was arrested by Iranian authorities in 2009 while he was serving as pastor in his church in the town of Rasht. A court sentenced him to death by hanging after convicting him of the crime of apostasy.

Apostasy is defined as the formal disaffiliation from or abandonment or renunciation of a religion by a person. Since Iran is an overwhelmingly Muslim country, its apostates (those who commit apostasy) would be those individuals who fall away from Islam, though the person who veers away from a particular faith towards another generally does not see him or herself as an apostate.

Islamic law in Iran stipulates that a Muslim who converts to another faith can face the death penalty. The Iranian Supreme Court upheld Naderkhani's sentence but said his conviction would be overturned if he repented and renounced his conversion, something he has refused to do on a number of occasions. If executed, Naderkhani would follow in the footsteps of early Christian martyrs, who refused to recant their faith on pain of death.

Dadkhah has argued against the death sentence for his client, saying, “…at the time of Prophet Mohammad no one was killed for being an apostate. The history of Islam shows that at the time of the Prophet three tribes became apostate but the Prophet didn't [order] them to be killed. There's nothing about killing apostates in the Koran."

The court is expected to hand down its final decision in the next few days.

The case has drawn international attention and criticism, especially from Britain and the United States. The U.S. has condemned Naderkhani’s conviction and called on Iranian authorities to release him. A White House statement reads, “That the Iranian authorities would try to force [Naderkhani] to renounce [his] faith violates the religious values they claim to defend, crosses all bounds of decency, and breaches Iran's own international obligations… A decision to impose the death penalty would further demonstrate the Iranian authorities' utter disregard for religious freedom, and highlight Iran's continuing violation of the universal rights of its citizens."

British Foreign Secretary William Hague said that he "deplored" reports that the pastor could be executed for not returning to Islam, while U.S. House Speaker John Boehner also urged Iran to grant Naderkhani "a full and unconditional release."

Iran has recently been cracking down on Christian proselytizing in the country, probably as a result of the increasing popularity of the religion. While a number of churches have reportedly been shut down and Christian converts arrested, no execution has been carried out thus far.

"There hasn't been an execution of a Christian pastor for apostasy for over 20 years but it seems like we're at the cusp of something and it really has to be deterred at this stage," said Dwight Bashir, the U.S. Commission on International Religious Freedom (USCIRF)’s deputy director for policy and research.

Naderkhani's wife was sentenced to life imprisonment, but has since been released.