Kenya's private sector activity slowed in June with its biggest contraction in close to a year, driven by slower consumer spending and the impact of protests during the month, a business survey showed on Thursday.

The Stanbic Bank Kenya Purchasing Managers' Index fell to 48.6 from 49.6 in May. Readings above the 50.0 mark indicate expansion in business activity while those below show contraction. The contraction was the sharpest in 11 months, the survey showed.

"Weaker conditions were primarily driven by a solid contraction in business activity. Survey respondents attributed this decline to lower customer spending, challenging economic conditions and operational disruptions from protests," Stanbic Bank said in comments accompanying the survey.

In the last week of June, thousands of Kenyans participated in protests, initially called to mark the anniversary of anti-government protests last year, but then amplified by public anger over the death during the month of a blogger in police custody.

Interior Minister Kipchumba Murkomen said at least 10 people had been killed during one day's unrest when youth-led demonstrations were followed by looting and arson in Nairobi and other cities.

The rights group Amnesty Kenya said at least 16 people were killed, all by gunshot, which it said was suspected to have been fired by police.

"The dip in activity was due to output and new orders contracting because of weaker consumer spending, challenging economic conditions, and social protests reappearing in June," Christopher Legilisho, Economist at Stanbic Bank.