The average cost of a litre of diesel at UK filling stations rose by 15.62p during June, according to RAC data.
The motoring organisation said the increase took the average cost of the fuel to 199.05p per litre.
The average price of petrol saw an even bigger increase during June, by 16.59p, to an average of 191.43p.
According to the RAC, higher pump prices were to be expected in June, as a result of the cost of oil rising during May, caused by a combination of increased demand for oil and concerns over supply because of the war in Ukraine.
However, the motoring organisation said the weekly wholesale costs paid by retailers had now been dropping for five straight weeks, yet these reductions had not yet been reflected at the pumps.
As well as calling on retailers to cut prices, the RAC also said the UK Government should temporarily cut fuel duty substantially or reduce VAT on fuel.
RAC spokesman Simon Williams said: “The rate at which pump prices have been rising over the last four weeks is hard to comprehend. Not a day in June went by when petrol prices didn’t go up, even though the price retailers pay to buy in fuel went down.
“There’s no doubt that drivers are getting an incredibly raw deal at the pumps at a time when the cost-of-living crisis is being felt ever more acutely.
“We badly need the government to go beyond just vague words and instead actually implement a clear package of financial support to show they’re on the side of drivers.”