Long-term borrowing costs across some of the world's biggest economies have hit fresh highs due to concerns over inflation, government debt levels, and spending on Artificial Intelligence (AI).

The interest rate on US borrowing over 30 years hit 5.33% on Tuesday, the highest since June 2007, while UK long-term debt reached 5.85%. There were similar moves in Germany and Japan.

Interest rates on bonds - which are a type of debt - are known as yields and can directly affect the borrowing costs consumers pay on mortgages, car loans and credit cards.

Rising oil prices are the main driver behind this recent surge in bond yields, as investors fear inflation could spike again.

If that happens, central banks may choose to raise interest rates to cool inflation.

On Tuesday, a barrel of Brent crude, the global benchmark for oil prices, surpassed $90 following growing tensions over the conflict in the Middle East.

The recent surge came after President Donald Trump threatened to bomb Oman - a US ally - if it "gets in the way" of talks with Iran to reopen the Strait of Hormuz waterway.

The US and Oman have each been negotiating separately with the Iranian government to reopen the key passage which is vital for global oil supply and other trade.

The strait being largely closed for almost six months due to the US-Israel war with Iran has caused oil supply disruption, leading to higher prices.

As well as hiking the cost of motor fuel, elevated global oil prices can lead to price rises across the board as companies pass the higher expenses they face to consumers, pushing up inflation.

Oil is a key factor in business. More often than not goods are transported by lorry or van.

John Canavan, lead analyst at Oxford Economics, told the BBC the inflation risk from higher oil prices, along with high levels of government debt and uncertainty around the vast sums being invested into AI - and when that will pay off - were all playing a part in higher borrowing costs.

He said this could lead to higher mortgage rates and borrowing costs for car loans for consumers as a result.

Higher yields, he warned, would mean companies could have to pay more to borrow money and might pass that on to customers.

"It adds to the overall inflationary impact," he said, adding that in the longer-term the risk was higher inflation could slow economic growth.

Bond investors typically demand higher returns - or yields - if inflation is high or they expect it to be elevated in the future.

Governments and corporations sell bonds - essentially an IOU - to raise money for spending and in return they pay interest.

As well as inflation fears, Canavan said there had been a "push back" across the world from bond investors over the broad financial policies and spending plans of a number of governments.

The UK's financial position and levels of borrowing has led to Prime Minister Andy Burnham to assure the bond markets that he is committed to sticking to the government's existing borrowing limits, known as its fiscal rules.

Borrowing costs edged up when he took over the Labour leadership from Sir Keir Starmer this summer.

Prior to commitments on the fiscal rules, investors had considered that Burnham would be more likely to increase Britain's already high public borrowing, especially following his comments last year that the UK had to "get beyond this thing of being in hock to the bond markets".

Economists at Capital Economics said in a note that the largest rises in long-term borrowing costs were being seen in the "US, UK, France, Italy, and Japan where, to varying degrees, the fiscal outlook is most problematic".

They said the situation did not represent a "bond market crisis", but added: "There are rational reasons for investors to demand higher returns on long-term government debt: greater geopolitical and inflation uncertainty, questions over US monetary policy and unsustainable fiscal positions."

Canavan said in long-term borrowing costs in the US were also being driven by a "record pace" of corporate borrowing in recent weeks, mostly for the development and build-out of AI and data centres.

However, with uncertainty over the hundreds of billions of dollars being ploughed into AI as well as the potential risks, investors are demanding higher returns on lending.

"The yields are troubling people because it portends a tighter environment and it's going to be more expensive to borrow money," said Kim Forrest, chief investment officer at Bokeh Capital Partners.

"Especially in this whole AI thing where time to pay it back is uncertain. It makes for a nervous investor environment."