Margaret Connolly is among at least six Irish citizens aboard the aid flotilla who have been detained by Israel, according to organisers, adding that it was intercepted approximately 70 nautical miles off Cyprus.

Speaking to reporters in London, President Connolly said she was worried about her sister.

“It’s quite upsetting, and I’m very worried about her, and I’m also very concerned about her colleagues on board

“I have been very busy today. I’ve been in the Irish Community Centre in Hammersmith, which was a wonderful, magnificent display.

“Then I met with King Charles. I haven’t really had a chance to get details in relation to my sister and, indeed, equally importantly, her colleagues on the boat,” she said.

Speaking in Irish, President Connolly pointed to how the incident took place in international waters, saying she was “proud” of Dr Connolly.

The flotilla has posted videos from Dr Connolly and five others, which appear to have been recorded in advance of their detention.

In her video, Dr Connolly said: “If you are watching this video, it means I have been kidnapped from my boat in the flotilla by the Israeli occupying forces, and I’m now being held illegally in an Israeli prison. 

"I am so proud to be taking part in this flotilla, it is the largest to date.”

Ireland must 'speak out' in face of injustice 

Last night in London, President Connolly told an audience at the Irish embassy in London that Ireland must “speak out in the face of injustice”.

She said Ireland brings “values we hold dear” to all relationships as a “neutral, independent, sovereign country”, which defends “international law and the structures of the United Nations, as enshrined in the UN Charter”.

“I look forward on this project and, in the years ahead, to building the next chapter of our relationship as neighbours, as friends, and as family,” President Connolly said.

“But also to use our voices in the world, a volatile world, to risk to say that normalising war is never acceptable, normalising slaughter is never acceptable.

“We have to use our voices to reclaim our language, not just in the sense of reclaiming our Irish language and our culture, but reclaiming our language so that language has meaning and that we can tell young people we mean what we say.”

President Connolly is in England as part of a three-day visit, which included a meeting with King Charles III yesterday afternoon at Buckingham Palace.

Following the meeting, she confirmed that she had invited the king to Ireland for a state visit — an invitation he “graciously accepted”.

She said that the king “knows Ireland well and has been a positive voice for peace and reconciliation”.

“Actually, I had a lot in common with the king in relation to the environment and climate change,” said President Connolly.

“We talked about the King’s Trust, the King’s Foundation, and many other [things], but I think the highlight really was the invitation that I extended to him as the 10th president of Ireland to make a state visit to Ireland.

“He graciously accepted that, so the details will emerge in due course between the two governments.”

President Connolly’s visit to England will continue today, and will see her visit the Chelsea Flower Show and the London Irish Centre in Camden.

The visit will conclude in Leeds tomorrow.

Louise Burne is Irish Examiner Political Correspondent, reporting from London.