Marine Le Pen, presidential candidate for France's far-right National Front party, has cancelled a meeting with Lebanon's grand mufti after refusing to wear a headscarf for the encounter.

"You can pass on my respects to the grand mufti, but I will not cover myself up," Le Pen told reporters on Tuesday.

The press office for the grand mufti said that Le Pen's aides had been informed beforehand of their requirement for her to wear head covering for the meeting.

Le Pen has been visiting Lebanon as she seeks to bolster her presidential credentials.

Opinion polls say Le Pen is likely to get the highest score in the first round of voting in April, but then lose to a mainstream candidate in the decisive second round vote in May.

AAP

On Monday, Le Pen met a foreign head of state for the first time, holding talks in Beirut with Lebanon's President Michel Aoun.

"We discussed the long and fruitful friendship between our two countries," the National Front (FN) leader said after her 30-minute encounter at the presidential palace in the hilltop suburb of Baabda with Aoun, the Middle East's only Christian president.

Le Pen, who is leading polls of voters' intentions for the first round of France's presidential election on April 23, said they also discussed the refugee crisis in Lebanon, where more than one million Syrians have fled their country's conflict and now make up one in four of the population.

"We raised... the concerns we share over the very serious refugee crisis," she said.

"These difficulties are being overcome by the courage and generosity of Lebanon but this cannot go on for ever."

The FN leader, whose party takes an anti-immigrant stance, called Sunday for the international community to step up humanitarian aid to keep the refugees in Lebanon.

Le Pen also met Lebanese Prime Minister Saad Hariri, a Sunni Muslim, who cautioned against associating his religion with the terrorist attacks of the jihadists who have repeatedly targeted France.

"The worst mistake would be the amalgam between Islam and Muslims on one hand and terrorism on the other hand," Hariri said, in a statement issued by his office.

"The Lebanese and Arabs, like the majority of the world, consider France to be the homeland of human rights and of the republican state that makes no ethnic, religious or class distinction between its citizens," he said.

On the refugee crisis, Hariri called on the international community "to assume its responsibilities".

Le Pen later had talks with Foreign Minister Gebran Bassil.

Emerging from that meeting, she told reporters asking her about the best ways of protecting the Christians of the Middle East: "Eradicating radical Islam."

"Protecting Christians means that they must be able to continue to live on their lands," she added.

Shunned by European leaders over her party's stance on immigration and its anti-EU message, Le Pen's meeting with Aoun aimed to boost her international credibility.

France had mandate power over both Lebanon and Syria during the first half of the 20th century.

Rival presidential hopeful and former French economy minister Emmanuel Macron visited Beirut on January 24, where he met both Aoun and Hariri.

Le Pen has met few top foreign officials since taking control of the FN in 2011. German Chancellor Angela Merkel has refused to meet with her.

And Spanish Prime Minister Mariano Rajoy told AFP last week that "a victory of the populists would be the end of Europe", a clear reference to Le Pen's call for a referendum on France's EU membership.