Opposition leader Raila Odinga and Mombasa Governor Ali Hassan Joho want an independent international agency to audit the lifestyles of top Kenyan leaders.
Joho said foreign auditors incapable of compromise should investigate governors, the President and Deputy President.
Raila urged the President Uhuru Kenyatta to be courageous in the war on graft.
The two ODM leaders also criticized Deputy President William Ruto and his entourage for launching early presidential campaigns and attempting to sabotage the national reconciliation efforts.
Raila claimed Ruto and his allies had tried to pour cold water on the mandate of the building bridges committee by attempting to suggest that it could not recommend far-reaching changes to how Kenya is governed.
Joho and the former prime minister spoke at Treasury Square in Mombasa, where thousands of Muslims and local politicians gathered for the Eid ul Fitr Baraza.
Backing a recent statement by Uhuru on the need to audit the lifestyle of leaders, the Opposition leaders, however, said the top brass should be handled to ensure transparency.
Raila said it would not be easy to probe the wealth of some powerful people in Government, but added that there was abundant evidence of graft involving top Government officials.
He claimed the rich and corrupt in Kenya were "pouring money all over" and could be apprehended even without much of a lifestyle audit.
Joho said the country would require an international audit organisation to handle the powerful political class, including the President, his deputy, cabinet secretaries and governors.