The Russian rouble weakened against the dollar after exporters completed their forex sales to meet Friday's monthly tax payment deadline.

Traders said Thursday's announcement by the central bank that it would reduce its daily foreign currency sales in the second half of the year - separate from the operations it conducts on behalf of the finance ministry - was also a factor weighing against the rouble.

On the interbank market, where liquidity can be low as major Russian banks that have been sanctioned cannot participate, the rouble traded 1.5% lower at 86.30 to the dollar by 0756 GMT.

The average dollar-rouble mixed composite rate, calculated by LSEG and based on data from international brokers and counterparties, stood at 86.24.

The central bank's official dollar-rouble rate was set at 84.96 for June 28, calculated on the basis of OTC trading.

Sanctions on Moscow Exchange and its clearing agent, the National Clearing Centre (NCC), have led to a range of varying prices and spreads after it halted exchange trading in the dollar and euro this month. Trade moved to the over-the-counter (OTC) market on June 14.

Russia's central bank said on Thursday it would sell 8.4 billion roubles ($97.4 million) worth of foreign currency per day in the second half of the year, down from 11.8 billion roubles in the first half.

The central bank's operations are conducted on the domestic forex market in Chinese yuan, and are related to the replenishment and spending of money from the state's rainy day National Welfare Fund.

The bank's own forex operations are separate from those it conducts on behalf of the finance ministry, for which in the current month it is buying the equivalent of 3.7 billion roubles a day of foreign currency.

On Friday the rouble was trading at 11.70 to the yuan, down 1.6%.

Brent crude oil, a global benchmark for Russia's main export, was up 0.7% at $86.96 a barrel. Traders said the firm oil price and expectations that the Russian central bank would increase its key rate at its July meeting would lend support to the rouble.

(Reporting by Reuters, writing by Mark Trevelyan; Editing by Anil D'Silva)