An anti-corruption group says Kenya's police force has been ranked the most corrupt institution in the country.

In a new report, Transparency International says the likelihood of Kenyans being asked for a bribe from police is 93 percent.

The international group says rampant police corruption threatens to make it socially acceptable to use alternative systems of  justice, such as illegally-armed groups, vigilantism and mob violence.

The report also shows that bribery across Kenya's government is on the rise, with 45 percent of respondents saying they paid bribes to speed up access to services, compared to 29 percent last year.

Kenya's president, Mwai Kibaki, has pledged to make fighting corruption central to his administration since he was first elected in 2002.

Some information for this report was provided by AFP.