Nigeria is close to breaking up and its leadership has descended into a "theatre of the absurd", according to the Nobel prize-winning playwright Wole Soyinka, who has been leading protests against the nation's political crisis.

The veteran writer and civil rights activist told The Independent that his home country was now a "failed state" where ordinary people's "anger has peaked", with potentially lethal consequences. "Nigeria is looking at its last chance in the next year," he said.

Africa's most populous country and leading oil producer is beset by multiple crises, from attacks by armed militants in the Niger Delta to sectarian massacres in its central region and a protracted struggle for the presidency in the capital, Abuja.

Mr Soyinka's warning came yesterday as the Movement for the Emancipation of the Niger Delta (Mend) – the leading militant group in the delta region – set off two car bombs.

"If nothing changes, I cannot guarantee what recourse the people will take," the writer said. "The level of anger has peaked. I don't rule out Nigeria breaking up. That's what can happen to a failed state."

Mr Soyinka, the first African to win the Nobel prize for literature, has been at the forefront of Nigeria's democracy movement since the country gained independence from Britain in 1960. Now 76, he is the figurehead of the Save Nigeria Group, which has brought thousands of people on to the streets to demand the impeachment of the critically ill President, Umaru Yar'Adua, who has not been seen in public for four months.

Mr Soyinka condemned what he called the "industry of lies" that had grown up around the President's medical condition. He said Nigeria's first lady, Turai Yar'Adua, who has denied access to her husband and kept his true condition a secret, should stand trial for her role in the power vacuum. "This woman is there standing guard against the truth of his health," Mr Soyinka said. "When will the rest of the nation wake up?"

Mr Yar'Adua was taken to hospital in Saudi Arabia in November and only came back to Nigeria last month. Since his return he has been kept in an ambulance; he is treated only by Saudi doctors and no one outside his wife's inner circle has seen him, including the acting president, Goodluck Jonathan.

"[The President] returns under the cover of darkness and they say he is up and drinking tea, with a straight face," Mr Soyinka added. "Everyone knows it is a lie – even those who say it – and it insults people's intelligence. His mother was told to go away and could not see her son. It is spousal abuse."

He accused Mrs Yar'Adua of using her husband's "phantom existence" for her own interests, along with a corrupt cabal of unelected leaders that he called a "bunch of absolute brigands". "It has gone beyond theatre of the absurd into something ghoulish going on macabre," the writer said.

Mr Soyinka said Nigeria had a failing "neocolonial constitution", a wave of "political assassinations" and was a place where power failures were "the norm" and its leaders were "robber barons" looting the country. "There is this myth of Nigerian resilience, that we will always pull back from the brink, but there is a critical mass at which some things implode," he said.

He defended the "real militants" in the Niger Delta, whom he said had a right to take on the government over decades of neglect, rights abuses, environmental crimes and theft of resources. He called Mend "a small, well-organised and resourceful militant group" that could choke the government's lifeline of oil. Yesterday, Mend launched its biggest attack since last year.

Mr Soyinka has been jailed twice under Nigeria's dictators: firstly in 1965 for taking over a radio station to denounce a rigged election, and again in 1967 after trying to mediate in the dispute that led to a civil war.

The author compared the task of reforming Nigeria to that of Sisyphus, saying: "You roll that damn rock up the hill, you don't get anywhere and the rock rolls back down."