The UK’s stock market has fallen sharply after a warning from two US banks triggered a widespread sell-off in global shares.

Two US regional lenders, Western Alliance Bank and Zions Bank, said on Thursday that they had been hit by either bad or fraudulent loans, sparking fears of problems in the banking sector.

Some of the UK’s biggest banks, including Barclays and Standard Chartered saw their share prices fall more than 5%. The FTSE 100 index of leading shares had dropped about 1.5% at one point before regaining some ground.

Stock market indexes around the world, including Germany’s Dax and the Cac 40 in France, also fell.

On Thursday, Zions Bank said it would write off a $50m loss on two loans, while Western Alliance disclosed it had started a lawsuit alleging fraud.

“Pockets of the US banking sector including regional banks have given the market cause for concern,” said Russ Mould, investment director at AJ Bell.

“Investors have started to question why there have been a plethora of issues in a short space of time and whether this points to poor risk management and loose lending standards.”

“Investors have been spooked,” he added, saying that while there was no evidence of any issues with UK-listed banks, “investors often have a knee-jerk reaction when problems appear anywhere in the sector”.

Bank shares in Europe were also hit, with Germany’s Deutsche Bank down more than 5% and France’s Societe Generale dropping 4%.

Investors have also been nervous following the failure of two high-profile US firms, car loan company Tricolor and car parts maker First Brands.

These failures have raised questions about the quality of deals in what is known as the private credit market – where companies arrange loans from non-bank lenders.

This week Jamie Dimon, the boss of the US’s largest bank JPMorgan Chase, warned that these two failures could be a sign of more to come.

“My antenna goes up when things like that happen,” he told analysts. “I probably shouldn’t say this, but when you see one cockroach, there are probably more. Everyone should be forewarned on this one.”

In addition, there have also been warnings that the surge in artificial intelligence investment has produced a bubble in the US stock market – including from Jamie Dimon – leading to fears that shares are overvalued.

The market turbulence on Friday saw the price of gold reach a fresh record high of $4,380 per ounce, as investors looked for safe havens for their money.

Another closely watched measure of market nerves, the VIX volatility index sometimes called the “Fear Index”, hit its highest level since April.