By Alexander Marrow

The rouble weakened against the dollar on Friday after the Bank of Russia hiked rates by a more-than-expected 100 basis points, pointing to rising inflationary pressures, with risk-off sentiment hitting Russian assets before the weekend.

The central bank's decision to raise its key rate to 8.5% surprised analysts polled by Reuters, although inflation data this week had prompted some to expect a larger increase than the 50-basis-point hike predicted on Monday.

The rouble was 0.4% weaker against the dollar at 90.62 by 1350 GMT, and had lost 0.2% to trade at 100.73 versus the euro. It had dropped 0.1% against the yuan to 12.59.

Higher rates should make investments in Russian assets more appealing, but they can have a negative impact on economic growth by making lending more expensive.

Pressure has intensified on the Russian currency after an abortive armed mutiny by the Wagner mercenary group in late June. Attacks on Russian infrastructure have also dampened risk appetite.

The central bank has blamed the rouble's weakness on falling exports and a rebound in imports. Russia's balance of payments was negative in June for the first time since 2020.

"That's bad news for the rouble," said Alfa Bank Chief Economist Natalia Orlova. "Another problem is that more and more export revenues are paid for in roubles," she added, meaning that Russia receives a reduced amount of its foreign trade surplus in foreign currency.

Central Bank Governor Elvira Nabiullina on Friday said the rouble rate was closely linked to rising domestic demand, a key inflation driver. Strong demand is pushing up imports, while exports are continuing to fall, she said.

Periodic bursts of capital outflows in response to political news have plagued the rouble since Russia invaded Ukraine in February 2022. Nabiullina said capital movement had not impacted the rouble rate recently.

An investor chat forum on Friday was full of comments about Moscow's decision to keep compulsory military service for 18-year-olds, permanently increasing the number of young men liable to conscription, after lawmakers dropped a proposal not to start before the age of 21.

"This topic is very sensitive for the market community as it directly affects this contingent (male traders of conscription age)," said a trader at a large Russian bank.

Higher oil prices, easing domestic demand for foreign currency and upcoming month-end tax payments by exporters should buttress the rouble.

Brent crude oil, a global benchmark for Russia's main export, was up 0.5% at $80.02 a barrel.

Russian stock indexes were mixed.

The dollar-denominated RTS index was down 0.1% to 1,015.8 points. The rouble-based MOEX Russian index was 0.1% higher at 2,920.6 points.

(Reporting by Alexander Marrow; Editing by Barbara Lewis, Jane Merriman, Louise Heavens and Mike Harrison)