A coordinator for the Irish delegation on the Global Sumud Flotilla has said she believes all of the Irish citizens aboard the flotilla have now been detained.
It is understood that 22 Irish citizens were on board the flotilla in total.
The Irish detainees were first held at Ashdod port for several hours last night before being brought to Ktzi'ot prison in the Negev desert, about an hour and 40 minutes from Ashdod near the border with Egypt.
Around half of the detainees have agreed to a voluntary deportation order.
The other half have said they will not agree to sign those forms.
They instead will appear before a judge in Israel who will issue a deportation procedure and will likely be deported at some stage next week.
Lawyers have been in touch with detainees and have been attempting to provide as much advice to them as possible.
A separate flotilla involving around 12 ships, with around seven Irish citizens onboard, is currently en route to Gaza.
The organisers of the flotilla have said they will do everything they can to ensure humanitarian aid arrives in Gaza.
Tánaiste Simon Harris said the Irish Government’s priority is securing the safety of the Irish detainees.
Mr Harris confirmed that a team from Ireland's Embassy to Israel, led by the Ambassador, had the opportunity to visit Ketziot prison
The Irish Ambassador to Israel Sonya McGuinness spent the day today at the Ktzi'ot prison ensuring that the Irish detainees get the legal protection and healthcare treatment that they need.
A delegation in Dublin is also providing ongoing updates to the families of those detained in Israel.
Speaking on RTÉ's Morning Ireland, coordinator of the Irish delegation of the flotilla Helen Lawlor said that organisers will pass information on to the families once they know it is credible and verified.
"Generally, what happens is they're offered various forms to sign. People choose themselves whether to sign the forms or not because the first form will say that they have entered Israel illegally, whereas none of these people have actually entered Israel illegally, they were all brought there against their will after being intercepted in international waters," she explained.
"If they don't sign those forms, they have the opportunity to go in front of a judge and have a hearing and be deported, generally maybe 72 to 96 hours afterwards.
"But we can never guarantee what will happen this time, because this is very different. People have been through this process before but never almost 500 people at one time."
Ms Lawlor said another flotilla is already on its way to Gaza and more will come.
Watch: Crew of Marinette, last ship of Global Sumud flotilla, give peace symbol on route to Gaza
"These flotillas will not stop until a humanitarian corridor is made on the sea to Gaza to get humanitarian aid into these people. There are Irish people on all of these flotillas ... either on the way to Gaza or being planned," she said, adding that she did not think it was "inevitable" the next flotilla would also be intercepted.
"Either humanity perseveres or governments step up and create this humanitarian aid corridor. The sea is a legal way of travel, and this is through international waters. None of these flotillas are doing anything illegal, these are all legal acts.
"It's absolutely preposterous to think that one government can control the whole world's reaction to a genocide. That's what's happening here. These flotillas will continue over and over and over again until aid gets into Gaza by the sea," she said.
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Organisers say last Gaza flotilla boat intercepted by Israel
The only remaining boat in the flotilla carrying aid to Gaza has been intercepted by Israel, organisers have said.
"Marinette, the last remaining boat of the Global Sumud Flotilla, was intercepted at 10.29 am (8.29am Irish time) local time, approximately 42.5 nautical miles from Gaza," the flotilla said on Telegram.
It added that Israeli naval forces had "illegally intercepted all 42 of our vessels - each carrying humanitarian aid, volunteers, and the determination to break Israel's illegal siege on Gaza".
The Global Sumud Flotilla - consisting of dozens of ships - set sail last month, ferrying politicians and activists including Swedish campaigner Greta Thunberg towards Gaza, where the United Nations says famine is taking hold.
The Israeli navy began intercepting the boats on Wednesday, and an Israeli official said yesterday that boats with over 400 people on board had been prevented from reaching the coastal territory.
The flotilla said today that 42 vessels had been "illegally intercepted" and their passengers "unlawfully abducted".
That left just one ship, the Marinette, pressing ahead with its mission to break the Israeli blockade of Gaza, according to the flotilla's tracker.
Watch: Cameras on board show the Marinette continuing to sail towards Gaza
"The world saw what happens when civilians challenge a siege. And still - Marinette sails on," the flotilla said on Instagram.
"She knows the fate of her sisters on the water. She knows what awaits. And she refuses to turn back."
Protesters around the world held rallies yesterday condemning Israel's interceptions and urging greater sanctions in response.
About 15,000 people marched in Barcelona - where the flotilla began its voyage - chanting slogans including "Gaza, you are not alone", "Boycott Israel" and "Freedom for Palestine".
Hundreds also gathered outside Leinster House in Dublin, where Miriam McNally, whose daughter was sailing with the flotilla, said she was "worried sick".
Protests also took place in Paris, Berlin, The Hague, Tunis, Brasilia and Buenos Aires.
Israeli Prime Minister Benjamin Netanyahu praised the interceptions.
"I commend the soldiers and commanders of the navy who carried out their mission on Yom Kippur in the most professional and efficient manner," he said in a statement.
"Their important action prevented dozens of vessels from entering the war zone and repelled a campaign of delegitimisation against Israel."
Gaza's civil defence agency and hospitals said Israeli strikes on the territory killed at least 52 people yesterday, including an employee of the French charity Doctors Without Borders.
Read more: Latest Middle East stories
The mother of one of the Irish activists said the participants are shining a light on Gaza.
Catríona Graham was detained after the vessel she was travelling on, the Aurora, was intercepted by Israel.
Her mother, Imelda, said all of Catríona's family were very supportive of her.
"We hope that she is well treated while she is in detention in Israel. The main thing is we really feel that she’s there on behalf of supporting Gaza as part of this humanitarian mission," she said.
"The whole flotilla, Catríona and her fellow activists are just so determined. I think they are a terrific focus for people all around the world to be able to deal with this awful situation which has been ongoing for the last two years.
"I think they give us all a voice, I think they give the common people a voice that they are this focus and this light on the awful things that are happening," Imelda said.
