The political party of Egypt’s Islamist president ousted by the military last year said Wednesday it considers the election of the former army chief as the next president “null and void” and will accept nothing short of the reinstatement of Mohammed Morsi.

The statement by the Muslim Brotherhood’s Freedom and Justice Party underlined the depth of the rift in Egypt as retired Field Marshal Abdel-Fattah el-Sissi prepares to be sworn into office on Sunday.

El-Sissi, then Egypt’s top officer, masterminded the removal of Morsi on July 3 after massive protests against the country’s first democratically elected president. Since then, the military-backed government has waged a crackdown on Morsi’s supporters that has killed hundreds, arrested thousands and shattered the Brotherhood, once Egypt’s strongest political organization.

El-Sissi was elected president with a landslide victory in a three-day vote held last week.

The Freedom and Justice Party said it “doesn’t recognize the alleged coup regime or any of its decisions that have been or will be issued since July 3 until the return of the elected President Mohammed Morsi to his post as the president of the Republic of Egypt.”

Al-Jazeera’s Egypt channel, meanwhile, said Wednesday that it had obtained a letter from Morsi, who has been detention since his ouster and is on trial on a number of charges, some of which carry the death penalty.

According to the channel, the letter labels el-Sissi’s election as a farce and calls on his supporters to continue their opposition to authorities. “Your revolution will be victorious in the near future,” Al-Jazeera quoted Morsi as writing.

The Muslim Brotherhood and its Islamist allies have held nearly daily protests demanding Morsi’s return, though they have been limited in recent months under the weight of the crackdown.

It did not say how the letter was obtained and there was no way to verify its authenticity.

“I spared no effort to fight corruption and crime, through the law at times but more often through revolutionary measures,” Morsi wrote, according to the station. Referring to the extraordinary measures taken by authorities to get the vote out in last week’s election, he said Egyptians “slapped them down … and humiliated them.”

Also Wednesday, the outgoing interim president gave an emotional farewell speech Wednesday, saying the public must rise to its responsibilities in the face of the country’s enormous challenges — echoing el-Sissi’s campaign theme that Egyptians must put end turmoil to allow reconstruction.

Adly Mansour said the country is “in better shape” today after the passing of an amended constitution and the presidential elections. But he said Egyptians must distance themselves from “personal interests, group demands or party inclinations” so the country can regain its strength.

The head of the Supreme Constitutional Court, Mansour was installed as interim president after Morsi’s ouster — and ended up serving almost as long as Morsi.

During that time — besides the turmoil of Islamist protests and the crackdown — a low-level militant insurgency in the Sinai spread to other parts of Egypt, targeting mostly police and military and killing hundreds. Militant groups said they are avenging the removal of Morsi and the crackdown.

Also, criticism grew among non-Islamists over signs the government was stifling other forms of dissent.