As he issued a call to young African leaders to break decades of violence and guide the continent towards prosperity and stability, Kerry warned it was never easy to negotiate with warring factions.
Talking to a Tanzanian activist who is working to bring together his community, Kerry said "the biggest challenge is trying to get many factions to cooperate to reach the same aim."
"Let me tell you something as somebody who's in the middle of trying to get some people to just get seven days of a ceasefire in the Middle East, I know what you're talking about Hashim," Kerry said with a wry laugh.
The top US diplomat, who returned to Washington late Sunday after failing to reach a ceasefire during shuttle diplomacy between Egypt and Israel, quoted late South African anti-apartheid icon Nelson Mandela saying "it's always impossible, until it is done. And that's what we have to have as our guide."
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Kerry was addressing the opening of a presidential summit for Young African leaders, and he vowed it was "time to take our partnership to the next level, by investing in the continent's greatest resource of all: its people."
"It is a time and a place where all of you have the great opportunity of a lifetime to bend the arc of history toward change, not stagnation," he told some 500 visitors from sub-Saharan Africa.
"You can bend it toward peace and prosperity, not conflict and retribution," he said.
He urged Africa's younger generation to "seize the future and become the next generation of CEOs and community and political leaders."
"This really is a moment of great opportunity for Africa. But make no mistake, it's not automatic. It is also a moment of great decision," the top US diplomat, speaking ahead of a major summit planned next week in Washington hosted by President Barack Obama, bringing together some 50 heads of state and government from across Africa.
"You will decide whether or not a decade of progress leads to an era of African prosperity and stability or whether your countries tragically fall back into cycle after cycle of tragic violence.