MOSCOW, July 8 (Reuters) - The Russian rouble briefly hit a three-week low against the dollar on Monday, but managed to halt a downward trend caused by reduced foreign currency inflows at the start of the month to strengthen marginally on the day.

The rouble reached 90.02 to the dollar, its lowest mark since June 14, the day after new U.S. sanctions on Russia's key financial market infrastructure were imposed, before bouncing back to 87.62 by 1507 GMT, up 0.4%.

The rouble has weakened steadily since late June, coinciding with reduced foreign currency supply from exporters who usually convert FX revenues into roubles to meet local liabilities towards the end of each month.

Sanctions on the Moscow Exchange and its clearing agent, the National Clearing Centre (NCC), 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.

Against the yuan, which had already become the most traded foreign currency in Moscow before the latest sanctions were imposed, the rouble strengthened by 0.4% to 11.93, according to an analysis of the OTC market.

The rouble gained 0.5% against the euro to 94.92.

Brent crude oil, a global benchmark for Russia's main export, was down 0.3% at $86.28 a barrel. (Reporting by Gleb Bryanski; Editing by Alexander Marrow and Timothy Heritage)