Perhaps an answer to your question...
"Reaction to the letter was mixed in Iran and across the Mideast.
Iranian newspapers described the message as "an initiative in global diplomacy" and "dialogue under the shadow of war."
But conservative lawmaker Hashmatollah Falahatpisheh lambasted Ahmadinejad for failing to consult parliament before sending the letter to the country Iran considers its greatest enemy.
"This message is the outcome of a series of taboo-breaking behaviors in Iran's foreign policy. ... That the parliament is not aware of (the contents of the) letter is questionable," Falahatpisheh told an open session of the parliament broadcast live on state-run radio Tuesday.
Among Gulf nations, the letter fueled suspicions toward Iran.
The Saudi-owned daily Asharq Al-Awsat called the letter proof that "Iran is not enriching uranium for peaceful purposes as it says, and is striving for leadership and control of the region."
Such Iranian leadership would mean the Israeli-Palestinian peace process "would be stalled, the Iraqi dream (of democracy) would be thwarted and we would witness a new wave of armament," wrote Tariq Alhomayed, the paper's editor-in-chief.
The Kuwaiti newspaper Arab Times ran an editorial in which editor-in-chief Ahmed Al-Jarallah accused Ahmadinejad of acting "as if he owns the region."
Some of Iran's Arab neighbors have expressed fears over Iran's nuclear program — particularly over pollution in case of an accident — as well as over the standoff with the West, fearing possible Iranian retaliation against American military bases in Kuwait, Qatar and Bahrain should the U.S. launch a pre-emptive strike."
Excerpted from http://news.yahoo.com/s/ap/20060509/ap_on_re_mi_ea/iran_us;_ylt=AtEAGs7k.dKwigmBeQ.V8nJI2ocA;_ylu=X3oDMTA5aHJvMDdwBHNlYwN5bmNhdA--
Who released this letter ?
Iran or the White House ?
Ahmadinejad's comments seem consistent with it being a final invitation to convert to islam (from your posted article):
As he boarded a plane for Indonesia on Tuesday, Ahmadinejad said his letter contained "the demands of Iranian people and our nation."
"I discussed our views, beliefs and positions regarding international issues as well as some ways out of problems humanity is suffering from," he told the official Islamic Republic News Agency. "We will wait for reaction ... and then we'll make decisions."
The repeated reference to "monotheism" in the letter is a typical way islamists approach the conversion of Christians, that is, in seeking to have them renounce the divinity of Christ.