Ahmed El-Hamrawi, a leading member of the Muslim Brotherhood, has resigned from both the group and its political wing, the Freedom and Justice Party (FJP), to protest the letter sent by Egyptian President Mohamed Morsi to his Israeli counterpart Shimon Peres.
The letter, which was sent on 17 October to introduce the newly-appointed Egyptian ambassador to Israel, provoked controversy due to its friendly wording.
"This message is national and religious treason, which disregards the blood that has been shed since 1948 at the hands of Zionists," read the resignation letter of El-Hamrawi.
El-Hamrawi, who has been a member of the Brotherhood for 28 years and was one of the original founders of the FJP, said that the letter has destroyed the history of the Muslim Brotherhood and all they believe in. It is unclear when El-Hamrawi resigned; however, the text of his resignation letter was published on private-owned daily Al-Masryeen on Saturday.
In the presidential letter, Morsi, who resigned from the Brotherhood upon becoming president, chose to address Peres as "great and good friend", according to the Times of Israel, which published a copy of the letter.
"We thought that Mubarak and his gang are the traitors, but it turned out to be that the circle of treason is much bigger. If Mubarak was Israel's treasure, then Morsi is their loyal friend, as described by his letter," added El-Hamrawi.
Presidential spokesperson Yasser Ali confirmed the authenticity of the letter on Friday, saying that the letter was following protocol.
Former assistant foreign minister Hani Khalaf told Ahram Arabic news website on Thursday that the terms of the letter might not have been chosen specifically.
"There is a template for such letters that is not amended with the change of officials, administrations or the country to which the letter is sent."
"As it is all routine procedure, the letter might come out of the foreign ministry to the general bureau without the president checking it," added Khalaf.
Prior to the January 25 Revolution, the Muslim Brotherhood had organised a number of protests to demand the expulsion of the Israeli ambassador to Egypt; the group had also organised several aid convoys to Gaza.