The incident occurred as supporters gathered in the arrivals hall to welcome six campaigners as they arrived on a flight from Turkey after having been detained by Israeli forces.

When a relative of one of the activists tried to approach them, a police officer forcefully prevented him from doing so, leading to scuffles between both sides, public broadcaster TVE reported.

Images broadcast by the station showed police striking people with batons at the airport and pinning others to the ground while being jeered by onlookers.

Four people were arrested for serious disobedience, resisting arrest and assaulting law enforcement officers, the Basque regional police force, the Ertzaintza, said in a statement.

“Following what happened at the airport, the Ertzaintza internal affairs division has launched an investigation to determine whether the officers’ conduct complied with procedures,” it added.

Two of those arrested were activists who had just arrived from Turkey, TVE reported.

Amnesty International condemned what it described as the “excessive use of force” by Basque police officers at the airport and called for “effective accountability” over the incident,

“The images published show no legitimate cause for the use of force,” it added in a statement.

“It is very serious that batons were repeatedly used against people who had already been knocked down and were on the ground.”

Hundreds of activists from countries around the world were detained in Israel after they were intercepted at sea on Monday while attempting to break the blockade of the Palestinian territory.

The group included 44 Spanish nationals, according to Spain’s foreign ministry.

Around 20 other activists from the flotilla landed at Barcelona airport on Saturday, where they were welcomed by supporters, including Culture Minister Ernest Urtasun.