The muscular display of power and pageantry at the inauguration in Washington may be watched by envious eyes around the world. Not least among those who yearn to build another USA – the United States of Africa – under a single president.

Such was the dream of Muammar Gaddafi, a quixotic project that appeared to have died with the Libyan dictator but has now been rekindled by the Zimbabwean president, Robert Mugabe.

Speaking in Harare after meeting Benin's president, Thomas Boni Yayi, who is the outgoing African Union (AU) chairman, Mugabe argued that a figurehead is needed to move Africa beyond regional blocs and into the global superleague.

"Get them to get out of the regional shell and get into one continental shell," he was quoted as saying by the state-owned Herald newspaper.

"The continent of Africa: this is what we must become. And there, we must also have an African head. He was talking of the president of Africa. Yes, we need one. We are not yet there.

"This is what we must go and discuss, but we must also discuss the issues that divide us."

The AU holds its latest summit this week in Addis Ababa, Ethiopia. Mugabe, 88, warned that Africans are not as united as was expected by the founders of the AU's predecessor, the Organisation of African Unity, half a century ago.

"We really have not become integrated as an African people into a real union," he said. "And this is the worry, which my brother has, and the worry I have; the worry perhaps others also have. That we are not yet at that stage which was foretold by our fathers when they created this organisation."

The founding fathers had a vision of a continent united politically, economically and culturally, he added. "We are not there yet. As we stand here people will look at us, as me anglophone, him francophone, you see. There is also lusophone, but we are Africans first and foremost. Africans, Africans. Look at our skin.

"That's our continent, we belong to one continent. We may, by virtue of history, have been divided by certain boundaries and especially by colonialism. But our founding fathers in 1963 showed us the way and we must take up that teaching that we got in 1963. That we are one and we must be united."

A United States of Africa spanning Cape Town and Cairo was proposed by Gaddafi in 1999 as a way of ending the continent's conflicts and defying the west, but it failed to secure enough support from his African counterparts. Some suspected that Gaddafi wanted the job for himself – a charge that Mugabe is hardly likely to dodge.

There is a case for challenging borders that were drawn up by European imperialists and which continue to inhibit travel and trade. But critics say the notion of uniting 54 countries with their thousands of languages and ethnicities is currently untenable. In fact some parts of Africa have been moving in the opposite direction and seeking local autonomy. Economies are moving at very different speeds.

Lindiwe Zulu, international relations adviser to South African president Jacob Zuma, said: "I don't foresee a single United States of Africa with a single president because we are so diverse politically and otherwise. It is very desirable in the long term but I don't see it any time soon. There is a lot more to be done. We are still agonising over sovereignty."

She added: "When you call for one president, you are calling for ministers to serve under them, one parliament and one legislative process. There are too many things that divide us on political, social and economic levels. We need to have a common agenda and approach to human rights and development before we can talk about one president. We need to deal with democracy on the continent and leaders who think beyond themselves."

Richard Dowden, director of the Royal African Society, said: "The idea that one government could rule the whole of Africa at this stage is silly and unworkable. They need to build from the bottom economically rather than imposing a notion of unity from the top down; it's absurd.

"It is a dream of totalitarian fantasists, not the people. Africa is becoming increasingly local. I'm in Kenya at the moment and the forthcoming election is all about ethnic arithmetic."