MOSCOW, June 21 (Reuters) - The Russian rouble weakened against the dollar in low liquidity on Friday, extending losses after its sharpest daily fall since July 2022 in the previous session, as markets reacted to last week's U.S. sanctions on key financial systems after some initial appreciation.

The sanctions on Moscow Exchange and its clearing agent, the National Clearing Centre (NCC), have led to a range of varying prices and spreads as trading shifted to the over-the counter (OTC) market on June 14, obscuring access to reliable pricing for the Russian currency.

On the interbank market, where liquidity can be low as major Russian banks that have been sanctioned cannot participate, the rouble traded 1.6% lower at 88.60 by 0817 GMT against the dollar.

The average dollar-rouble mixed composite rate, calculated by LSEG and based on data from international brokers and counterparties, stood at 87.35, demonstrating a wider spread - the difference between buying and selling prices.

The central bank's official dollar-rouble rate was set at 85.42 for Friday, calculated on the basis of OTC trading.

The rouble strengthened sharply after the sanctions were imposed amid low liquidity, caused by various technical difficulties to do with interbank limits when closing FX deals on the OTC market and as traders closed foreign currency positions.

Thursday's drop was likely a response to strong appreciation earlier in the week.

"We assume that the key factor was the strong, oversold rouble and market participants' expectations of swift actions to normalise the situation on the FX market by the regulator and government, which are long overdue," said Promsvyazbank's Yevgeny Loktyukhov.

Capital controls that have been supporting the rouble since October were softened on Friday, with the government reducing the volume of foreign currency revenue that exporters must convert into roubles to 60% from 80%.

Against the yuan, the rouble shed 1.8% to 12.13, according to an analysis of the OTC market.

The yuan had surpassed the dollar to become the most traded currency with the rouble in Moscow before last week's sanctions were imposed. It accounted for a 54% share of the FX market in May.

Brent crude oil LCOc1, a global benchmark for Russia's main export, was 0.3% lower at $85.47 a barrel. (Reporting by Alexander Marrow; Editing by Shinjini Ganguli)