By Andrey Ostroukh

MOSCOW--Russia's services sector activity contracted for the first time in three months in June, reflecting spare capacity amid weak consumer demand, a Markit survey of purchasing managers showed Friday.

The Purchasing Managers' Index for the services sector fell to 49.5 in June from 52.8 in May, sliding below the 50 mark, which separates growth from contraction.

"The PMI data for Russia continue to underwhelm, with slight falls in activity registered across the private sector in June. As spare capacity remains evident, jobs subsequently continue to be cut," Paul Smith, senior economist at Markit, said in the PMI report.

Markit said majority of services sector companies left their output prices unchanged in June, which sent the inflation rate to a 10-month low.

Despite a volatile ruble and Western sanctions, the PMI survey showed that businesses in the services sector remained optimistic in June for the fourth month in a row. A number of the polled companies said they were forecasting better macroeconomic environment, both domestically and globally.

"Compared to earlier in the year, operating conditions have shown some relative stability during recent months. Companies are hoping that this will provide a platform for future growth, with service providers forecasting growth of activity over the coming year - subject to a general pick-up in the wider economic environment," Mr. Smith said.

Earlier this week, another PMI survey showed that activity in Russia's manufacturing sector deteriorated marginally in June, as output, new orders and employment all fell.

Write to Andrey Ostroukh at andrey.ostroukh@wsj.com