The leader of French far-right Front National (FN) party has suggested that four hostages released by al-Qaida after years in captivity might have turned into Islamists because they sported long beards.

Marine le Pen said she was puzzled by the look of Pierre Legrand, 28, Daniel Larribe, 62, Thierry Dol, 32, and Marc Féret, 46, who were freed in the African Sahel by Islamist militants three years after they were abducted.

"I found those images bewildering," Le Pen told Europe 1 radio, commenting footage showing the four being greeted by President Francois Hollande when they landed at Paris Villacoublay military airport.

"I've found their extreme privacy astonishing and their clothing astonishing; I felt uneasy watching those images; I believe I wasn't the only one," said L Pen.

None of the four men wanted to speak after Hollande addressed journalists on the tarmac and some were made visibly uncomfortable by the intense media attention.

"Two of them sported a beard-cut that is at least baffling," she added. "One had a scarf covering his face."

The four Frenchmen were abducted by al-Qaida's northern African branch, al-Qaida in the Islamic Maghreb (AQIM), in 2010, while they were working in Arlit, Niger, where the French nuclear giant Areva operates a uranium mine.

It is believed they spent the last three years being dragged around the Sahel, the arid region that stretches from the Atlantic Ocean to the Red Sea just south of the Sahara Desert which is prowled by AQIM militants.

"I'm not a psychiatrist. I've just expressed what I felt," Le Pen replied after being asked if she believed the four ex-hostages had converted to Islam. "It is not my role to make theories."

"However it is not forbidden to think that they might be victims of the Stockholm syndrome," Le Pen later told Le Figaro newspaper.

Her comments were criticised and ridiculed on social media with some netizens saying she had watched too many episodes of the American TV series Homeland, in which the main character, a former US marine, converts during captivity.

"Marine le Pen had just finished a marathon of #Homeland," tweeted @n_manth.

"Marine le Pen thought the hostages were going to step off the plane with a three piece suit and a bow tie," wrote @Cheikouuu.

The four were rescued in northern Mali, where French troops have been fighting off an Islamist insurgency led by several rebel groups including AQIM.

They were reportedly retrieved in a desert area near the border with Mauritania and Algeria by a team of 18 Frenchmen and Tuaregs.

The French government said their release was brokered by Niger's president Mahamadou Issoufou and no military operation was involved, nor money was paid.

However sources close to the operation claimed France paid up to €25m ($34m, £21.5m) in ransom.

French hostages hollande
French President Francois Hollande with former hostages, Marc Feret, Pierre Legrand, Daniel Larribe, Thierry Dol on the tarmac at Villacoublay military airport (Reuters)