Tech stocks slide on AI doubts, oil jumps after attacks

Oil has surged by more than three per cent and bond prices have tumbled as renewed fighting in the Middle East and US sanctions on Iranian crude threatens the ceasefire, while stocks have wobbled on concerns the record AI rally might be running short on buyers.

Brent crude futures climbed 3.3 per cent on Wednesday, the most in a day since late May, to $US76.54 a barrel.

While that was well shy of the peaks above $US120 during the height of the fighting, it was enough to inject some fresh inflation risk into the bond market, particularly since months of conflict have drawn down global oil inventories.

"Obviously the market doesn't like these attacks ... but it's not full-blown panic mode," said Jason Wong, senior strategist at BNZ in Wellington.

The US said it hit Iranian air defences, coastal surveillance and drone launch sites, and Iran's Revolutionary Guards said they targeted the US military in Bahrain and Kuwait, where air raid sirens sounded on Wednesday.

Washington also moved to withdraw a concession allowing Iran to sell oil on the global market, which Iran's foreign ministry said breached the framework deal to end the war.

Benchmark 10-year US Treasury note yields rose for a seventh day in a row to a one-month high of 4.56 per cent, while in Europe, yields on German and Italian 10-year bonds also hit one-month highs at 3.04 per cent and 3.85 per cent, respectively.

"Just when we thought we could put the geopolitical risk premia to bed ... we were certainly reminded that this peace deal is very much still a process," said David Chao, Asia-Pacific global market strategist at Invesco in Singapore.

"I think where Brent (is) currently, it's still trading at levels that I think are not factoring in some of the continued flare-ups from the Middle East."

Data showed stocks of crude in the US Strategic Petroleum Reserve hit their lowest level since 1983, leaving markets more vulnerable to future supply shocks.

European markets opened under pressure on Wednesday, with the STOXX 600 down 0.8 per cent, as healthcare and consumer stocks were sold, offsetting gains in oil and gas shares.

US and European stock futures were down 0.2 per cent to 0.3 per cent.

Asian markets were volatile and swung to losses as investors were rattled by Samsung Electronics shares sliding for a second straight session, despite the company flagging a staggering 19-fold rise in profit.

Analysts and investors are concerned that memory chip demand may slow in the second half of the year.

In the past couple of weeks, there has been a distinct shift out of red-hot chip stocks and into other parts of the market, including financials, consumer stocks and back to the so-called hyperscalers that have dominated market action over the past year or so.

Samsung's results highlighted how investors are increasingly questioning valuations as bottlenecks in some parts of the AI supply chain - such as memory chips or data centres - start to clear, and pricing for AI models becomes harder to predict.

In currency markets, the dollar held steady, leaving the euro just above $US1.14 and the yen hovering about 162, not far from 40-year lows.

Minutes from last month's Federal Reserve meeting are due later on Wednesday, and traders reckon new chair Kevin Warsh might pare back the detail to dampen any policy signal.