Spain’s foreign ministry has demanded the immediate release of a Spanish national it said was being “held illegally” by Israel after the interception of a Gaza-bound flotilla, hours after an Israeli court moved to extend his detention by two days.

Saif Abu Keshek, who lives in Barcelona, and Thiago Ávila, from Brazil, appeared in court in Ashkelon on Sunday, days after Israeli forces intercepted at least 22 boats from a flotilla that was attempting to break Israel’s maritime blockade of the devastated Palestinian territory to deliver aid.

The interception took place in international waters off Greece. Israel later said it had removed 175 activists from the Global Sumud Flotilla, which was made up of about 58 vessels carrying crew members from 70 countries. Two members of the flotilla, Abu Keshek and Ávila, were later taken to Israel for questioning.

On Sunday, the rights group representing the pair said the court had ruled to extend their detention and that no formal charges had been filed against them. “The court extended their detention by two days,” Miriam Azem, the international advocacy coordinator at Adalah, told Agence France-Presse.

A source from Spain’s foreign ministry told the Guardian on Sunday that the Spanish consul in Tel Aviv had attended Abu Keshek’s court hearing, adding that he was being “held illegally”.

His next hearing was scheduled for Tuesday, the source said, adding: “The Spanish government demands his immediate release.”

On Saturday, Adalah said its lawyers had met the two detained activists at Shikma prison in Ashkelon.

The right group said Ávila had told the lawyers he had been “subjected to extreme brutality” when the vessels were seized, saying he had been “dragged face-down across the floor and beaten so severely that he passed out twice”.

Since arriving in Israel, Ávila said he had been “kept in isolation and blindfolded”, according to Adalah.

Abu Keshek, meanwhile, had been “hand-tied and blindfolded … and forced to lie face down on the floor from the moment of his seizure” until reaching Israel, the group said. “Both activists are continuing their hunger strike in protest of their unlawful detention and ill-treatment,” it added.

Israel’s foreign ministry has accused the two activists of being affiliated with an organisation that is subject to US Treasury sanctions.

Washington accuses the Popular Conference for Palestinians Abroad (PCPA) of “clandestinely” acting on behalf of the Palestinian militant group Hamas.

Israel’s foreign ministry accused Abu Keshek of being a leading PCPA member and alleged that Ávila was also linked to the organisation and “suspected of illegal activity”.

On Friday, after it emerged that the two men had been taken to Israel for interrogation, Spain and Brazil issued a joint statement condemning what they described as the “abduction of two of their citizens in international waters by the government of Israel”.

The Spanish and Brazilian governments demanded the immediate return of their citizens, adding: “This flagrantly illegal action by the Israeli authorities outside their jurisdiction constitutes a violation of international law, which could be brought before international courts, and may constitute a crime under our respective national laws.”

Spain and Israel have long been at diplomatic odds, particularly as the Spanish prime minister, Pedro Sánchez, emerges as one of Europe’s most vocal critics of Israel’s war in Gaza.

Speaking at a political rally on Saturday, Sánchez condemned the detention of Abu Keshek and Ávila. “We have seen that the Israeli authorities under [Benjamin] Netanyahu’s government have kidnapped several citizens who were on the flotilla heading to Palestine to deliver humanitarian aid and to continue reminding the world that there are people suffering in Gaza, in the West Bank, and throughout Palestine,” he said.

Sánchez added: “Now that Netanyahu has done this – kidnapping foreign citizens, one of them Spanish – and taken him to Israel, I have several things to say to Prime Minister Netanyahu. The first is that Spain will always protect its citizens. The second is that we will always defend international law, and this is a new violation of international law. And the third is that we want the release of the Spanish citizen who has been illegally kidnapped by the Netanyahu government.”

Organisers of the flotilla said the Israeli interception took place more than 620 miles (1,000km) from Gaza and that their equipment was smashed, leaving them grappling with what they called a “calculated death trap at sea”. The Israeli military declined to comment when asked about the accusations by AFP.

The Global Sumud Flotilla’s previous attempt to reach Gaza in the summer and autumn of 2025 drew global attention after Israeli forces intercepted the boats off the coasts of Egypt and Palestinian territory. Crew members including the Swedish activist Greta Thunberg were arrested and expelled by Israeli forces.

The flotilla’s latest attempt came as a senior UN official said the humanitarian needs in Gaza remained “overwhelming.” About 1.8 million people – almost the entire population of Gaza – were displaced and dependent on aid, while hostilities continued and public health risks were mounting, Khaled Khiari, an UN assistant secretary general, told the security council last week.

Gaza, which is governed by Hamas, has been under an Israeli blockade – described by the UN as “a direct contravention of international human rights and humanitarian law” – since 2007.

Israel’s war in Gaza, triggered by the Hamas attack on 7 October 2023, has led to severe shortages of food, water, medicine and fuel, and killed more than 72,500 Palestinians, according to aid agencies.

AFP contributed to this report