Along with McKinney, who served six terms in the House of Representatives from Georgia and was the Green Party’s presidential nominee in 2008, Israeli authorities took 20 people into custody, the group said.

Also aboard, the group said, was Mairead Maguire, who co-founded a group that worked for peace in Northern Ireland. Maguire and co-founder Betty Williams received the Nobel Peace Prize in 1977 for their work.

IDF said the Israeli navy contacted the boat, which it called the Arion, while it was still at sea and warned the crew they would not be allowed to enter Gazan waters “because of security risks in the area and the existing naval blockade.”