Kenya's opposition Saturday called a fresh anti-government rally for next week to protest rising prices and taxes after three previous demonstrations largely failed to mobilise supporters.

Last week saw a trio of protests against the administration of President William Ruto, taking the total of such marches to eight since March.

But while a rally on Wednesday saw sporadic incidents in several towns, and some 300 arrests according to the interior ministry, further protests Thursday and Friday ended in a damp squib despite scuffles between marchers and police in Nairobi's largest slum area of Kibera, an opposition stronghold.

"There will be a new demonstration next Wednesday," Dennis Onyango, spokesman for veteran opposition leader Raila Odinga, told AFP.

Ruto on Thursday urged a halt to the demonstrations, saying they were "not a solution to the problems of Kenyans".

The authorities have banned a number of rallies in March, April and July but some ended in violence, with 20 deaths, according to official sources.

Rights groups including Amnesty International on Friday denounced "repression" by police and said they had evidence of 27 "extrajudicial, summary and arbitrary executions" in July alone.

The UN, the Commonwealth and media have urged Ruto and Odinga to engage in dialogue.

The home of the son of former president Uhuru Kenyatta, whom Ruto served as vice-president for a decade, was raided on Friday, with the interior ministry saying authorities were searching for weapons.

Kenyatta backed Odinga in last year's election rather than his former vice-president and authorities say he supports the protest marches.

Ruto is under increasing pressure amid a spiralling cost of living and the announcement of a number of tax increases.

Odinga, who contested last year's election outcome, called off demonstrations in April and May after Ruto agreed in principle to a dialogue which has failed to materialise.