By Dan Merica, CNN

Washington (CNN) - The White House Thursday condemned the conviction of an Iranian pastor, who may be executed in Tehran for refusing to recant his religious beliefs and convert from Christianity to Islam.

Pastor Youcef Nadarkhani "has done nothing more than maintain his devout faith, which is a universal right for people," a White House spokesman said in a statement. "That the Iranian authorities would try to force him to renounce that faith violates the religious values they claim to defend, crosses all bounds of decency and breaches Iran's own international obligations."

The United States Commission on International Religious Freedom, an independent advisory group appointed by the president and Congress to monitor religious freedom around the world, Wednesday expressed "deep concern" for Nadarkhani, the head of a network of Christian house churches in Iran.

After four days of an appeals trial for apostasy, Nadarkhani refused to recant his beliefs, the commission said. Chairman Leonard Leo said the pastor "is being asked to recant a faith he has always had. Once again, the Iranian regime has demonstrated that it practices hypocritical barbarian practices."

While the trial is closed to the press, Leo said the commission collects information from sources in Iran and around the world.

The commission's statement also called the trial a sham and said Iran is violating the International Covenant on Civil and Political Rights, to which it is a party.

"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," the White House statement said. "We call upon the Iranian authorities to release Pastor Nadarkhani and demonstrate a commitment to basic, universal human rights, including freedom of religion."

Nadarkhani was first sentenced to death in November 2010, the commission said, and in order to avoid the death penalty, he is being asked to recant his beliefs and convert to Islam. Leo said an apostasy trial is rare in Iran; the last occurred in 1990.

Iran's claim stems from the pastor's Muslim parents. According to Leo, the court needed to verify if Nadarkhani had ever been a Muslim. In order to be given what Iran claims is the opportunity to recant his beliefs, Nadarkhani must have never been a Muslim before the age of 15, Leo said.

Because he was given the opportunity during the four-day trial, it is apparent that the Iranian court found he was never a Muslim and therefore Nadarkhani could have converted.

According to a source close to the situation within the Commission on International Religious Freedom, Ayatollah Ali Khamenei, the Supreme Leader of Iran, would have to sign off on the execution. Speaking on the condition of anonymity because of the subject's sensitivity, the source said such cases in Iran are difficult because of the lack of transparency in leaders' decision-making.

The source also said that in the past, political prisoners have had their prison time and punishment reduced by the Iranian government. Though they did not say that was guaranteed in this situation, the source indicated it was a possibility.

The American Center for Law and Justice, a right-leaning organization founded by television evangelist Pat Robertson, reported Wednesday night that Nadarkhani's death sentence had been overturned, meaning that the pastor would be receiving a lesser punishment. They sourced the claim to someone in Iran.

Those reports could not be independently verified by CNN. The Permanent Mission of the Islamic Republic of Iran in the United Nations failed to comment on the ruling.

Jordan Sekulow, executive director of the ACLJ, said the outcry from Christians in America has been loud and sustained.

"American Christians, like never before, are engaged in this," Sekulow said. "This is evidence that Christians in America over the past decade have done a better job engaging in the persecution issue."