The human rights group has told Sky News the 34-year-old's sentence may have been annulled but fears remain he will be put to death.
A spokesman said: "We've had some reports that there has been a verbal announcement from the court in Iran that the sentence is annulled but we urge caution.
"It's been known that verbal announcements have been directly contradicted by later written statements. We are still calling for international pressure to be kept up."
Sky sources say Nadarkhani was given a verbal assurance last year that he would not be sentenced to death but then was.
The case centres on alleged apostasy - the abandonment or renunciation of one's religion.
Pastor Nardarkhani was born to Muslim parents but did not practise the faith and then converted to Christianity when he was 19.
“I am resolute in my faith and Christianity and have no wish to recant.”
Christian Iranian Pastor Youcef Nadarkhani
The text of your message begins here...He became a member of the Protestant evangelical Church of Iran and held services in "home churches" in the town of Rasht.
In 2009, he fell foul of the authorities when he challenged the law which insists that all schools should teach Islam.
He was arrested in October 2009 and a year later was sentenced to death for apostasy on a charge which has doubtful legality in the Iranian civil legal system, but which is underpinned by sharia law.
Pastor Nardarkhani pleaded not guilty, partially on the grounds that from puberty he was never a practising Muslim and thus had not renounced his faith.
But he has denied that Muhammad was the prophet of God.
He has been given three opportunities to renounce his Christianity but refused saying: "I am resolute in my faith and Christianity and have no wish to recant."
Among those campaigning to save him is the British Foreign Secretary William Hague. He has said: "I pay tribute to the courage shown by Pastor Nadarkhani who has no case to answer and call on the Iranian authorities to overturn his sentence."
\ã-'sir-é-ä\ n (1998)
1: an ancient empire of Ashur
2: a democratic state in Bet-Nahren, Assyria (northern
Iraq, northwestern Iran, southeastern Turkey and eastern Syria.)
a democratic state that fosters the social and political rights to all of
its inhabitants irrespective of their religion, race, or gender
4: a democratic state that believes in the freedom of
religion, conscience, language, education and culture in faithfulness to the
principles of the United Nations Charter —
Ethnicity, Religion, Language
Israeli, Jewish, Hebrew
Assyrian, Christian, Aramaic
Saudi Arabian, Muslim, Arabic
\ã-'sir-é-an\ adj or n (1998)
1: descendants of the ancient empire of Ashur
2: the Assyrians, although representing but one single
nation as the direct heirs of the ancient Assyrian Empire, are now
doctrinally divided, inter sese, into five principle
ecclesiastically designated religious sects with their corresponding
hierarchies and distinct church governments, namely, Church of the
East, Chaldean, Maronite, Syriac Orthodox and Syriac Catholic.
These formal divisions had their origin in the 5th century of the
Christian Era. No one can coherently understand the Assyrians
as a whole until he can distinguish that which is religion or church
from that which is nation -- a matter which is particularly
difficult for the people from the western world to understand; for
in the East, by force of circumstances beyond their control,
religion has been made, from time immemorial, virtually into a
criterion of nationality.
the Assyrians have been referred to as Aramaean, Aramaye, Ashuraya,
Ashureen, Ashuri, Ashuroyo, Assyrio-Chaldean, Aturaya, Chaldean,
Chaldo, ChaldoAssyrian, ChaldoAssyrio, Jacobite, Kaldany, Kaldu,
Kasdu, Malabar, Maronite, Maronaya, Nestorian, Nestornaye, Oromoye,
Suraya, Syriac, Syrian, Syriani, Suryoye, Suryoyo and Telkeffee. —
1: a Semitic language which became the lingua franca of
the Middle East during the ancient Assyrian empire.
2: has been referred to as Neo-Aramaic, Neo-Syriac, Classical
Syriac, Syriac, Suryoyo, Swadaya and Turoyo.