Kenyan President Uhuru Kenyatta on Saturday endorsed his former arch-rival for the country's top job, weeks after their parties joined forces ahead of presidential and parliamentary elections in August.

"We have chosen Raila Odinga without any opposition to be the fifth president of Kenya," Kenyatta told a cheering crowd numbering thousands in the capital Nairobi.

The announcement brings together two of Kenya's top political dynasties, who have a long history of opposing each other at the ballot box.

But in 2018, Kenyatta and Odinga stunned the country when they shook hands and declared a truce after post-election violence in 2017 left dozens of people dead.

Last month, Kenyatta's Jubilee party announced that it would join the Azimio la Umoja (Quest for Unity) coalition headed by Odinga.

On Saturday, Kenyatta declared his backing for the veteran opposition leader, saying: "We don't have any doubt that we have a team captain in Raila Amolo Odinga."

Odinga, 77, responded, saying he accepted "the nomination with absolute gratitude and dedication to our people."

The announcement came after Kenyatta's anointed successor William Ruto, who also intends to contest the presidential election, was sacked from Jubilee.

Ruto was initially anointed by Kenyatta as his successor but found himself marginalised after the 2018 pact between the president and his former foe.

With its diverse population and ethnic voting blocs, elections in Kenya have often been marred by violence.

More than 1,100 Kenyans lost their lives in 2007 when a disputed election result sparked tribal violence.

Odinga and Kenyatta have unsuccessfully tried to introduce sweeping constitutional changes, claiming that the reforms would help to end repeated cycles of election violence.

The reforms -- popularly known as the Building Bridges Initiative (BBI)-- proposed expanding the executive and parliament to more evenly divide the spoils of victory.

But it was seen by critics as a way to enable Kenyatta -- a two-term president who cannot run for a third -- to remain in power by establishing the post of prime minister.

The government has appealed a court ruling that rejected the proposals and said Kenyatta could even be sued in a civil court for launching the process.