Assange is wanted in the US for allegedly violating the Espionage Act by publishing military and diplomatic files in 2010, and could face up to 175 years in jail if found guilty, though the exact sentence is difficult to estimate.

Ahead of voting on Sunday, Melenchon was asked about the extradition of Assange to the United States, which the British government approved on Friday to the dismay of his supporters and free-press campaigners.

"If I am prime minister on Monday, Mr Julien Assange -- I believe he has already asked for it -- will be naturalised as French and we will ask for him to be sent to us," Melenchon told reporters.

"Mr Assange should be decorated for all his services to French people," he added.

Melenchon's new NUPES coalition of left-wing and green parties is hoping for a majority after Sunday's vote, which could lead to 70-year-old Melenchon being named prime minister.

But polls suggest centrist President Emmanuel Macron's "Together" coalition is likely to emerge as the biggest party.

The French parliament debated a motion in February proposing granting Assange political asylum, which was defeated after failing to win enough support from Macron's MPs.

The WikiLeaks founder has influential contacts inside the current French government, however, with his former lawyer Eric Dupond-Moretti now serving as justice minister.

Dupond-Moretti had requested a meeting with Macron in 2020 in order to ask for political asylum for his client, and has faced calls from French rights groups to make good on his promise now that he is inside the cabinet.

Assange has 14 days to appeal the UK government decision, which came after a British court issued a formal order clearing his removal in April.

His supporters have held frequent rallies to protest the planned deportation, which they see as an infringement on media freedom and free speech.

He has been detained at a top-security jail in southeast London since 2019 for jumping bail in a previous case accusing him of sexual assault in Sweden.

In February 2020, Dupond-Moretti, one of France's best-known lawyers before he entered politics, called the possible 175-year prison sentence "shameful, unbearable and contrary to the idea everyone has of human rights."