On Tuesday G7 leaders agreed to explore "the feasibility of introducing temporary import price caps" on Russian fossil fuel, including oil, and tasked ministers to evaluate the proposal urgently.
A day later, Germany's envoy to the EU told his counterparts in a restricted meeting that the world should be "realistic" about the proposal, which he said was added to the G7 statement after "intense pressure" from Washington, according to one official who attended the meeting.
The envoy also said an agreement on whether to apply caps was not expected to come anytime soon, according to the source.
Hungary and Belgium also raised concerns at the meeting about the G7 statement on sanctions, the official said, with Hungary explicitly backing Berlin's caution on oil price caps.
A second EU official familiar with the talks confirmed that Germany and others had expressed wariness about oil price caps.
A spokesperson for Germany's embassy to the EU declined to comment.
A German government official said on Thursday that "success of this plan depends on international cooperation".
Stefano Sannino, secretary general of the EU's diplomatic service said on Thursday that a price cap would only be effective if universally applied, and so agreement would be needed across the G20 countries, not just the G7.
"You need to be sure you do not have distortion of trade and then the only thing that is happening is that essentially oil goes to other places with other carriers and insured by other companies - and so the price remains the same," Sannino told an EU-UK Forum conference.
Under EU sanctions that will become effective in December, insurance and other financial services crucial for Russian oil shipments will be banned worldwide.
Critics of this fear it could lead to higher global oil prices because of the key role EU companies play in shipping insurance, bringing a benefit to Moscow.
A cap, if agreed, would effectively make it possible for companies to trade Russian oil, instead of facing a total ban.
However, the EU sanctions on Russian oil, which took weeks to agree, would have to be tweaked and reopening the debate on this measure could be controversial, officials said.
(Reporting by Francesco Guarascio @fraguarascio; Additional reporting by John Chalmers; editing by David Evans)
By Francesco Guarascio