Oil prices tumbled back to pre-war levels Wednesday as recession fears returned to the forefront.

Stocks were also hit by the negative outlook for the global economy, while currency markets were gripped by the prospect for interest rate hikes.

Oil prices briefly climbed on Wednesday as Russia's President Vladimir Putin said his country would stop delivering oil and gas supplies to countries that introduce price caps.

G7 industrialised powers have vowed to move urgently towards implementing a price cap on Russian oil imports to cut off a major source of funding for Moscow's military action in Ukraine.

But oil prices then turned sharply lower, with Brent crude, the main international contract, passing under $90 per barrel for the first time since February.

OPEC and its allies earlier this week cut production targets for the first time in more than a year in a bid to lift prices.

"While the 100,000 barrel cut wasn't fundamentally significant, it was clearly intended as a warning not to drive the price lower or face further cuts," said OANDA trading platform analyst Craig Erlam.

"Unfortunately, it seems traders are in no mood to be told what to do and growth fears are instead dictating the price direction."

Recession concerns also dampened sentiment towards equities, with European indices lower, although Wall Street managed small gains at the open.

"Investors appear reluctant to buy anything in this macro environment, where inflation is soaring, global growth is weakening, and central banks are tightening," said City Index and FOREX.com analyst Fawad Razaqzada.

"Something must fundamentally change before we see the onset of a serious recovery," he added.

Recession fears are being driven in large part by central banks moving aggressively to rein in surging inflation.

The dollar continues to gain strength from expectations of a third-straight blockbuster hike to US interest rates later this month.

US Federal Reserve officials have lined up in recent weeks to say their main focus is bringing inflation down from four-decade highs, even if that means tipping the economy into recession.

The different pace in lifting rates taken by central banks is fuelling swings in currency values.

The European Central Bank is Thursday forecast to deliver another bumper rate increase, mirroring aggressive moves by the Fed and Bank of England.

Nevertheless, it has moved slower and the euro remains lodged below parity with the dollar.

Meanwhile, the dollar rose to 144.99 yen -- the Japanese currency's weakest showing since 1998.

"The reason that we are seeing this much strength in the dollar against the yen is purely because of the difference in two central banks' policies," noted Naeem Aslam, chief market analyst at AvaTrade.

"The Fed is as hawkish as it can be, and the BoJ still doesn't seem to be bothered much about inflation or changing its stance on monetary policy."

Japan's finance minister, Shunichi Suzuki, on Wednesday expressed concern about the yen's drop.

"For now, we're monitoring with a sense of urgency how it's developing, but if this continues, it makes sense that we will take necessary measures," he said, without detailing what the measures might be.