Twenty-five activists detained while trying to reach Gaza by sea arrived in the Spanish and Portuguese capitals Sunday, where they were greeted by hundreds of people holding banners and Palestinian flags.

Some 450 activists were arrested as Israeli forces intercepted the Global Sumud Flotilla, a fleet of 42 boats seeking to break Israel’s naval blockade of Gaza and deliver a symbolic amount of aid to the famine-stricken territory.

Those detained between Wednesday and Friday were brought to Israel, where many remain in prison.

Among them was Mariana Mortágua, the leader of the Portuguese political party Left Block, who arrived in Lisbon with three other returnees.

Mortágua had to temporarily suspend her mandate to take part in the flotilla.

The four activists denounced what they claimed was mistreatment by Israeli authorities while in detention.

Meanwhile, dozens of family members and supporters crowded the Madrid International Airport arrivals hall to welcome the activists home on Sunday.

"There was some dehumanizing and violence and shouting but we got the European treatment. It doesn't compare to the torture that Palestinian people are facing," said Roos Ykema, a Dutch flotilla returnee, at Madrid International Airport.

Israel’s Foreign Ministry, meanwhile, has said the claims of mistreatment were “brazen lies.”

The Israeli Foreign Ministry said it offered voluntary deportation to all of the activists and those that remain in detention chose to stay there in order to go through a legal deportation process.

The arrests led to criticism from several governments including Turkey, Colombia and Pakistan.

The interception of the flotilla came as U.S. President Donald Trump attempted to broker a fresh ceasefire initiative in Gaza, as he ordered Israel to stop bombing Gaza.

Israel said it had accepted Trump's proposal, and Hamas has said it accepts some aspects. Negotiators are expected in Cairo on Monday.

AP video shot by Helena Alves and Alicia León Perea