My decision to resign is voluntary on my part and arises from my concern for the welfare of the people of Zimbabwe and my desire to ensure a smooth, peaceful and non-violent transfer of power that underpins national security, peace and stability.
Mugabe, 93, was placed under house arrest by the military several days ago.
Mugabe had been teetering on the brink of political ruin since the country's military seized power in the capital Harare, on Wednesday.
But now, with Mugabe refusing to resign despite repeated attempts at persuasion, and with parliament threatening to begin impeachment proceedings Tuesday, the military could be on a long and complicated path with a formidable opponent: Mugabe himself.
Protesters calling for the impeachment of President Robert Mugabe brandish a national flag as they demonstrate outside the parliament building in Harare, Zimbabwe, Nov. 21, 2017.
The military took action after the president fired his vice president, Emmerson Mnangagwa, a hero of Zimbabwe's liberation war, and hinted he would replace Mnangagwa with his wife, Grace Mugabe.
Mugabe steps down after 37 years as Zimbabwe's leader
Although many expected Mr Mugabe to announce his resignation on Sunday evening in his televised statement, it has now been reported that Zanu-PF decided he would not step down in front of the military generals and instead his speech was created to show the military intervention was not a coup.
Two days after that, on November 17, Mugabe made his first public appearance since the alleged house arrest.
Mugabe's resignation marks a major turning point in Zimbabwe's history. He has led Zimbabwe since a guerrilla struggle ended white-minority rule in the country formerly known as Rhodesia.
Following the army's intervention last week in response to Mugabe's sacking of vice president Mnangagwa, it has become clear that Mugabe's 37-year tenure as the Zimbabwean president will shortly come to an end amid widespread demands for his resignation.
This is a breaking news story.
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