Kenya's top two presidential contenders will face off against each other in polls Monday for the first time, but bring with them a long history of rivalry from political dynasties dating back more than half a century.

Uhuru Kenyatta, deputy prime minister and son of Kenya's first president, is neck-and-neck in opinion polls with Raila Odinga, prime minister and son of the first vice-president and later longtime opposition leader.

Fifty years since independence in 1963, the rivals say they would rather focus on the present than talk about the past but the weight of history -- and bad blood between their fathers -- remains.

"Uhuru Kenyatta is very aware of how his father became president and treated Odinga's father and vice versa," said Mwalimu Mati, a leading civil society figure and anti-corruption activist.

The two fathers, Jomo Kenyatta and Jaramogi Oginga Odinga, both now dead, started out as allies in the struggle for Kenya's independence from British colonial rule.

Kenyatta senior embodied that struggle. He was imprisoned by the British before becoming Kenya's first president.

Odinga senior worked to have Kenyatta freed and went on to become the country's first vice president.

But a rift soon developed. When Jaramogi Odinga, who was close to the Soviet Union, started to favour a redistribution of wealth and notably of land, Kenyatta -- who had become a top Western ally -- slammed him and fellow "radicals".

Jaramogi Odinga resigned in 1966. He was kept away from the seat of power, never to be allowed back into the entourage of Kenyatta, and was either banned from taking part in elections or placed under house arrest, both under Kenyatta and his successor Daniel arap Moi.

His son Raila Odinga suffered from his family's isolation, a potential driving factor for him to enter politics in the opposition.

He was imprisoned three times, the first in 1982, accused of taking part in a failed coup against Moi.

But unlike his father, Raila Odinga managed to mend fences with his rivals from time to time. Towards the end of Moi's reign, he made his entry into government as energy minister.

In 2005 he campaigned alongside Uhuru Kenyatta against constitutional reform.

Uhuru Kenyatta, with his family's vast riches and real estate empire behind him, had a smoother ride into politics, entering in the 1990s when Moi started grooming him as a successor.

But the 2005 alliance between Raila and Uhuru, as they are called to distinguish them from their fathers, did not last.

By the time the 2007 presidential poll came round, the two men -- the first the leader of the Luo community and the second a leader of the Kikuyu community -- were on opposing sides.

Kenyatta backed Mwai Kibaki, and Odinga ran against Kibaki but lost.

Odinga and Kenyatta finished up as prime minister and deputy prime minister respectively in the unity government that followed the 2008 post-election violence.

But there has been no real thaw in relations, particularly given that only one of the two, Kenyatta, was indicted by the International Criminal Court for his alleged role in the 2007-8 violence.

If obliged to talk about the past, the two prefer to linger over their previous alliances and to play down the times they fought.

"I don't think that we should try to draw a parallel because we are living in a very different time," Odinga told AFP in a recent interview.

"In those days there was a lot of polarisation, Kenya was just emerging from colonial rule and this was the era of the Cold War."

But for Peter Kenneth, another presidential candidate, the history is clear, saying that "their battles remind me of their fathers' battles 45 years ago."

For some observers, the paths of the two men symbolise a Kenyan political system that is short of new blood.

"Kenya is changing all the time, demographically, economically, but its political class was formed in the 1960s and then again in the 1990s," said Daniel Branch, an academic who wrote a recent book on Kenya's history since independence.

"Kenya isn't the same place as it was 50 or even 20 years ago, but its leaders don't reflect those changes that have taken place."