When a relative of one of the six returning activists tried to approach them at Bilbao airport on Saturday, a police officer forcefully prevented him from doing so, leading ​to scuffles between both sides, images from state broadcaster TVE showed.

Images showed ​police striking people with batons and pinning others to the ground ⁠while being jeered by onlookers. Before this, activists appeared to have blocked the ​exit for other passengers, and police tried to move them.

The Basque regional police ​force said in a statement on Sunday that it had launched an investigation to determine if officers complied with procedures. Reuters has reached out to the Spanish government for comment.

On Sunday’s march, ​pro-Palestinian demonstrators carried banners criticising the Basque police force and accusing the ​local government of being complicit with Zionism.

The activists were released from Israeli custody after being detained ‌on ⁠a flotilla trying to bring aid to Gaza.

Organisers alleged on Friday that the activists were subjected to abuse while in Israeli detention, with several hospitalised with injuries and at least 15 reporting sexual assaults, including rape.

Israel’s prison service denied the ​allegations, and Reuters ​was not able ⁠to verify the activists’ claims independently.

Spain was among a series of Western governments on Thursday which expressed their anger after Israeli ​minister Itamar Ben-Gvir posted a video of himself mocking the ​activists as ⁠they were pinned to the ground in a prison.

Francesca Albanese, a UN expert on the Palestinian territories, has called for those responsible for events at Bilbao airport ⁠to be ​held responsible, while Amnesty International has demanded a ​thorough investigation.

The Israeli Embassy in Spain has demanded an “explanation” from the Spanish government over the events ​at Bilbao airport.