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The plunging value of the Russian rouble has led game maker Valve to impose limits on its online store.

It has started putting "region-locks" on games bought via its Steam service in Russia so only people in that country can play them.

The move is an attempt to stop people outside the country buying games that are far cheaper from the Russian store.

Many games costing $40 (£25) on the US Steam store cost only a few dollars in Russia.

The Steam Prices website, which logs price differences across the regional Steam game networks, reveals many games are currently up to 10 times more expensive in the US and UK than they are in Russia.

Falling oil prices and economic sanctions have conspired to cause the value of the rouble to lose more than half its value against the US dollar this year. Earlier this week one dollar was worth 79 roubles though the currency has recovered since and now $1 buys about 61 roubles.

Valve's move is the first time that region locks have been imposed on games available via the hugely popular Steam service. Valve has yet to issue a comment on its decision to lock games.

Earlier this week Apple also reacted to the economic turmoil in Russia by halting sales made via the Russian version of its online store. It said exchange rates were too volatile for it to set prices.