MOSCOW, Aug 28 (Reuters) - The Russian rouble was flat

against the U.S. dollar on Wednesday but was set to weaken in

the coming days against both the dollar and the yuan as

exporting companies were expected to withdraw from the market

after paying their rouble taxes.

At 0745 GMT, the rouble was flat at 91.50 to the

dollar, according to LSEG data. The rouble fell as much as 9%

against the dollar earlier in August after Ukraine's surprise

attack on Russia's Kursk region, before stabilising around

current levels.

Trading in major currencies in Russia shifted to the

over-the-counter (OTC) market, obscuring price data, after

Western sanctions on the Moscow Exchange and its clearing agent,

the National Clearing Centre, were introduced on June 12.

According to an analysis of the OTC market, the rouble

weakened by 0.5% to 11.84 against the Chinese yuan, which has

become the most traded foreign currency in Moscow. The rouble

strengthened by 3% against the yuan in the last week.

Foreign currency sales by exporting companies to accumulate

enough roubles to pay their taxes at the end of the month are a

major factor affecting the currency market. The tax payments are

due today.

One-day rouble-dollar futures, which trade on the Moscow

Exchange and are a guide for OTC market rates, were up 0.1% at

90.63. The central bank's official exchange rate, which it

calculates using OTC data, was set at 91.48 to the dollar.

The rouble was 0.2% stronger at 102.14 against the euro

, according to LSEG data.

Brent crude oil, a global benchmark for Russia's

main export, was down 0.1% at $79.51 a barrel after a sharp drop

in the previous session ended a three-day streak of gains, amid

persistent concerns over potential supply losses from the Middle

East.