A new rule that prohibits Germany's petrol stations from hiking prices more than once day is unlikely to bring down costs for motorists, consumer experts said on Thursday one day after the restriction took effect.

"At the moment, it doesn't look as though the new rule will actually make filling up any cheaper," Ramona Pop, head of the Federation of German Consumer Organizations, told dpa.

Indeed, the average price for a litre of diesel fuel jumped to an all-time high on Wednesday, reaching €2,327 (around $2.67) as the new rule came into force, according to figures by the ADAC motoring organization published on Thursday.

The average price for a litre of Super E10 petrol also rose on Wednesday, reaching €2.129, the highest level recorded so far this year, according to ADAC.

In response to soaring oil prices as a result of the war in the Middle East, the German government passed a bill last week to limit petrol stations to raising prices once a day - at midday - to limit price fluctuations and ensure greater transparency. Price reductions will still be allowed at any time.

Many petrol stations increased prices significantly when the rule took effect on Wednesday.

Consumer expert Pop said that, under the new restrictions, it appeared that prices spike at midday and then fall back over the course of the day and the following morning.

"Consumers can save money by filling up in the late morning," she said.

"However, this time is inconvenient for most working people," she noted, calling on the government to quickly reassess the rule, including the timing of price adjustments.

The ADAC criticized Wednesday’s price rises as unreasonable, given that the price of crude oil fell between March 31 and April 1.