"We are hunting those who have converted to Christianity or Zoroastrianism as we consider them renegades and God's punishment must be implemented by killing them," said a statement posted on the al-Farouk website on 22 April and signed by al-Qaeda in Iraq.
The statement, whose authenticity could not be immediately confirmed, also urged the youth to join "[the] Mujahedin and hoist the jihad flag against the crusaders who are occupying Iraq, instead of supporting them."
"We are not afraid of them; in fact, they are welcome if they want to kill us," said Sabeer Ahmed, 37, who converted to Christianity seven months ago and works at Christ Church in the town of Pishdar in Sulaimaniyah province.
"We will be happy to be martyrs when we sacrifice ourselves for our religion," said Ahmed who works as a freelance journalist with Kurdish media groups.
According to Ahmed, about 500 Kurdish Muslim youths have converted to Christianity since 2006 throughout Kurdistan. It is not known how many, if any, have converted to Zoroastrianism, once a dominant religion in much of Iran. The faith has now dwindled to very few followers.
Muslim residents of Sulaimaniyah say the conversions were motivated by economic gain, as many of the youths in the area are unemployed.
"Missionaries are exploiting the harsh economic situation that these youths experience in these areas as they are unemployed and almost depressed," said Sheikh Hassan Abdullah, 57, one of the Sulaimaniyah elders.
"In some cases, the youths want to go abroad and this [conversion to Christianity] is an easy way to achieve their dream as they can say that they are threatened and need a safe haven," Abdullah added.
A priest in Sulaimaniyah, who refused to be named because of the sensitive nature of the issue, denied Christians were exploiting the harsh economic conditions of young people or that they were promising them material gains to convert to Christianity.
"Those youths [converts] reached their decision after having become fully convinced about what Christianity teaches. They believe in Christ and nothing else and we're sure of that," the priest said.
"This is their decision and no one forced them to convert. We do not accept anyone who seeks only material gain," he added.
Local officials in Iraq's Kurdistan refused to comment.
Humanitarian aid "cover"
After the US-led invasion of Iraq in March 2003, Sunni and Shia religious leaders said that US missionaries, mainly evangelicals, were pouring into predominantly Muslim Iraq shrouded in secrecy or under the guise of providing humanitarian aid.
Sheikh Ahmed al-Shafie, a member of the hardline Association of Muslim Scholars in Sulaimaniyah, denounced it as a "negative phenomena in an Islamic country" and blamed the "weakness" of Islamic propaganda.
"We strongly condemn this disgraceful act against Islam and Muslims which demonstrates that there are hidden hands with foreign agendas [working] to destroy the society of this country," al-Shafie told IRIN.
"We have a real weakness in our Islamic propaganda owing to the difficult situation our country is facing, and that makes many of our youths convert to Christianity after defaming Islam as a terrorist religion," he added without naming the foreign agents.
Another priest in Baghdad who also refused to be named said there had been "extensive efforts by US religious organisations immediately after the  invasion of Iraq but now these efforts had faded as many churches were attacked and closed by extremists hunting down Christians."
Following the 2003 US-led invasion of Iraq, the Jedda-based World Muslim League (WML) said that some "non-Muslim organisations" might exploit the humanitarian crisis in the country.
"Non-Muslim organizations are preparing to enter Iraq to start their activity under the cover of providing humanitarian aid, as they normally exploit crises, wars and tragedies, "WML Secretary-General Abdullah bin Abdumohsen al-Turki said.
He warned of "the dangers this poses to Muslims in Iraq" and called on the Iraqi people to adhere to Islam and to stay away from "ethnic and sectarian feuds."
In March 2004, four US missionaries were killed in a drive-by shooting in the northern city of Mosul.