Paris police said they had arrested two people in connection with the action, according to the AP news agency.
In footage of the incident, the pair are demanding the right to “healthy and sustainable food” saying “our agricultural system is sick”.
They shout: “What’s the most important thing? Art, or right to healthy and sustainable food?
“Our farming system is sick. Our farmers are dying at work.”
The pair then cross a boundary between the painting and public and stand beside the artwork, their right hands held up in a salute. Staff rush in to cover up the mess, propping up black protective panels.
Both protesters wore a T-shirt saying Riposte Alimentaire, which translates as ”food counterattack” and is the name of the activist group who have taken responsibility for the stunt.
They describe themselves as a collective which seeks to highlight the need to protect sustainable food.
A statement sent to the AFP news agency says the action marks the “start of a campaign of civil resistance with the clear demand... of the social security of sustainable food”.
The Louvre said that members of the group sprayed pumpkin soup on the painting at around 10:00am local time (09:00 GMT), and that there was no damage.
It said the Salle des Etats, where the work is displayed, was evacuated at the time and reopened to visitors shortly after at 11:30am local time (10:30 GMT).
They added: “The museum will lodge a complaint.”
— CLPRESS / Agence de presse (@CLPRESSFR) January 28, 2024
The image, which is more than 500 years old, sits behind protected glass since the 1950s to protect it after an acid attack. It was upgraded to armoured glass in 2005.
French Minister of Culture Rachida Dati sent her support to staff at the Louvre and said that “no cause can justify it being targeted”.
In a post on X, formerly known as Twitter, she said: “The Mona Lisa like our heritage belongs to future generations.”
After the incident, management at the Louvre opened a crisis unit, closing the room holding the Mona Lisa for cleaning.
The action comes after days of protests by farmers over rising fuel costs and changing regulations. Cabbages, tomatoes and other food was seen strewn across the highway as their protest entered its second week.
In 2022, a cake was thrown at the image in a demonstration against climate change. A man disguised as an elderly woman in a wheelchair threw cake at the famous painting.
The perpetrator, wearing a wig and lipstick, called on people to “think of the Earth” as they were led from the scene.