US President Barack Obama yesterday condemned tyrants who enrich themselves and urged Africans to demand stronger governments as the son of an African immigrant made a landmark trip to the continent.

On his first official trip as president to the heart of Africa, Obama vowed more US help to battle disease and said conflicts such as the "genocide" in Darfur and terrorism in Somalia were "a millstone around Africa's neck".

The US president, whose father was Kenyan, said these conflicts needed a global response.

"Africa's future is up to Africans," Obama said in a speech to the Ghanaian parliament which he hoped would resonate across the continent, before visiting a former fort from where countless slaves were shipped to the Americas.

But he added many warnings to Africa's leaders and its people.

"Development depends upon good governance. That is the ingredient which has been missing in far too many places, for far too long," he said.

"That is the change that can unlock Africa's potential. And that is a responsibility that can only be met by Africans."

"Repression takes many forms, and too many nations are plagued by problems that condemn their people to poverty. No country is going to create wealth if its leaders exploit the economy to enrich themselves, or police can be bought off by drug traffickers.

"No business wants to invest in a place where the government skims 20 per cent off the top, or the head of the Port Authority is corrupt. No person wants to live in a society where the rule of law gives way to the rule of brutality and bribery. That is not democracy, that is tyranny, and now is the time for it to end."

"Africa doesn't need strong men, it needs strong institutions," he declared to applause. Obama said he had instructed his administration to put a greater focus on corruption in its annual human rights reports. Obama highlighted "genocide" in Darfur and "terrorism" in Somalia as crises that have to be battled by the whole world.

"Africa is not the crude caricature of a continent at war. But for far too many Africans, conflict is a part of life, as constant as the sun.

"There are wars over land and wars over resources. And it is still far too easy for those without conscience to manipulate whole communities into fighting among faiths and tribes. These conflicts are a millstone around Africa's neck."

He praised Ghana's contribution to international peacekeeping forces but said the United States and other countries must help strengthen Africa's capacity to bring security.

"When there is genocide in Darfur or terrorists in Somalia, these are not simply African problems - they are global security challenges, and they demand a global response."

Obama offered diplomatic, technical and logistical support for efforts to improve security and "to hold war criminals accountable".

The US president also spoke of a "comprehensive, global health strategy" to help Africa confront the Aids pandemic and other diseases which kill millions each year on the continent.

"When children are being killed because of a mosquito bite, and mothers are dying in childbirth, then we know that more progress must be made," he said.

Obama also called on western nations to open up their markets to African goods to help their economies.

He said it was up to Africa's young people, in countries where they make up more than half the population, to change the continent.

"You have the power to hold your leaders accountable, and to build institutions that serve the people," he said. "Yes you can," he declared in a variation of his election campaign slogan.

Obama was warmly received in Ghana by thousands of people who poured onto the streets of the capital to catch a glimpse of him.

He chose Ghana as his first trip to sub-Saharan Africa because it was an example of a "functioning democracy" in a conflict-scarred continent.

Crowds waved flags and placards with slogans such as 'Obama you are the true son of Africa, we love you'.

He and his wife Michelle, a descendant of African slaves, as well as their daughters Malia and Sasha, later toured Cape Coast Castle, once one of Africa's main outposts from where slaves were shipped to the Americas.

Obama described the tour "a moving experience".

Key quotes from Obama's speech

Africa's future
"We must start from the simple premise that Africa's future is up to Africans. I say this knowing full well the tragic past that has sometimes haunted this part of the world. I have the blood of Africa within me, and my family's own story encompasses both the tragedies and triumphs of the larger African story."

Good governance
"Development depends upon good governance. That is the ingredient which has been missing in far too many places, for far too long. That is the change that can unlock Africa's potential. And that is a responsibility that can only be met by Africans."

Africa doesn't need strong men
"Across Africa, we have seen countless examples of people taking control of their destiny, and making change from the bottom up... Make no mistake: history is on the side of these brave Africans, and not with those who use coups or change constitutions to stay in power. Africa doesn't need strong men, it needs strong institutions."

Fighting Aids
"Building on the strong efforts of President Bush, we will carry forward the fight against HIV/Aids. We will pursue the goal of ending deaths from malaria and tuberculosis, and eradicating polio."

Ending genocide, terrorism
"Now let me be clear: Africa is not the crude caricature of a continent at war. But for far too many Africans, conflict is a part of life, as constant as the sun. There are wars over land and wars over resources. And it is still far too easy for those without conscience to manipulate whole communities into fighting among faiths and tribes. These conflicts are a millstone around Africa's neck. That is why we must stand up to inhumanity in our midst. When there is genocide in Darfur or terrorists in Somalia, these are not simply African problems - they are global security challenges, and they demand a global response. That is why we stand ready to partner through diplomacy, technical assistance, and logistical support, and will stand behind efforts to hold war criminals accountable."

Yes you can
"I am particularly speaking to the young people. You have the power to hold your leaders accountable, and to build institutions that serve the people. You can serve in your communities, and harness your energy and education to create new wealth and build new connections to the world. You can conquer disease, end conflicts, and make change from the bottom up. You can do that. Yes you can. Because in this moment, history is on the move."