Macron visited Ms May at her Downing Street office in London on February 21. He was photographed arriving and leaving, and spoke to reporters and TV crews in front of the building.
Asked in an interview, due to be aired on British radio station LBC later on Wednesday, whether she thought this was overt support for Macron and a snub towards her, Le Pen said: "It seems to be the case."
The British government says it has a long-standing policy not to engage with Le Pen's Front National party which has been considered toxic for decades by many mainstream European parties.
According to a transcript of the LBC interview, which was conducted by anti-EU British politician Nigel Farage, Le Pen said the decision to host Macron was inconsistent with May's own stance on delivering Brexit and reducing immigration to Britain.
Le Pen said Macron, who is strongly pro-EU, represented "the opposite of what Brexit stands for and the choice made by the British people".
Polls suggest Macron and Le Pen are likely to face each other in the run-off of the French presidential election on May 7, with Macron likely to win by a wide margin.
Farage suggested to Le Pen that Ms May's attitude towards her would change if she won the French election, drawing a parallel with Britain's dealings with US President Donald Trump. He said Downing Street had not wanted to engage with Trump until after he was elected.
Le Pen responded: "She is good at getting it wrong but this is rather reassuring."
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