A senior Russian ambassador is to meet an official from the Foreign Office on Thursday after the Prince of Wales caused a diplomatic row by comparing Vladimir Putin to Adolf Hitler.

The Prince made his remark, in which he likened Russia’s annexation of Crimea to the actions of Nazi Germany, during a visit to a museum of immigration in Halifax, Canada.

He told a woman whose relations were murdered in the Holocaust: “And now Putin is doing just about the same as Hitler.”

Russian diplomats contacted the Foreign Office on Wednesday night seeking an urgent meeting to clarify whether Prince Charles’s provocative remarks amounted to an “official position”.

As a result, Russia’s deputy ambassador will meet a senior FCO official on Thursday, The Telegraph understands.

The comments are regarded as particularly offensive by Moscow as 20 million Russians were killed during the war, including members of Mr Putin’s family.

A senior Russian diplomatic source said: “We are seeking clarification [from the FCO] at a working level. It’s not clear if it is an official position. The response from Clarence House is it was a private talk. We hope there is nothing behind it. But it is unclear to us: what does it mean? He is the future king, after all.”

The source added: “It is very serious. Every family in our country lost someone in that war.”

After years of thaw, including the awarding of medals to the British veterans of the Second World War Arctic Convoys, British and Russian relations were put into “deep freeze” after the Russian occupation of Crimea.

The European Union and US responded with sanctions on Russian MPs and the suspension of defence deals.

The Russian president has sought to revive the memory of the “Great Patriotic War” in order to bolster his reputation as the leader of a resurgent Russia. Prince Charles and Mr Putin are due to appear together at the anniversary of the D-Day landings in France next month.

Nick Clegg has defended the Prince over his comparison, saying that the heir to the throne is “entitled to his views”.

The Deputy Prime Minister told BBC Breakfast: “I have never been of the view that if you are a member of the Royal family somehow you have to enter into some sort of Trappist vow of silence. I think he is entitled to his views.”

Not every MP was as sympathetic. Mike Gapes, the Labour MP and member of the Commons foreign affairs committee, said: “In a constitutional monarchy, policy and diplomacy should be conducted by Parliament and Government. Monarchy should be seen and not heard.” The Russian media took a stronger stance, warning that the Prince’s comment could “trigger an international scandal”.

The Moskovskij Komsomolets, a popular Russian daily, said that the Prince had risked complicating already “not unclouded” UK-Russian relations.

Mr Putin’s spokesman, Dmitry Peskov, declined to comment on the issue. A spokesman for Clarence House said: “We do not comment on private conversations. But we would like to stress that the Prince of Wales would not seek to make a public political statement during a private conversation.”