A Nobel Peace Prize winner seized on an aid flotilla to Gaza earlier this year was stopped from entering Israel today.
Campaigner Mairead Maguire was detained in Tel Aviv airport after arriving in the country as part of a women's peace delegation.
The Nobel Women's Initiative, an organisation co-founded by Ms Maguire and five other Nobel peace laureates, planned the trip to meet women involved in peace initiatives in Palestine and Israel.
Professor Jody Williams, who is due to travel to Tel Aviv as part of the delegation later, said the group was concerned over her detention.
"We are very concerned that a committed fellow activist is being refused into the country," she said.
"Mairead's dedication to peace should not be considered a threat to national security."
Ms Maguire, who was told she was being repatriated rather than deported after being prevented from entering Gaza on the flotilla in May, is appealing the denial of entry. A court is expected to decide if she can enter.
She had been on board the MV Rachel Corrie in June when it was boarded by Israeli forces off the coast of Gaza.
Nine people were killed the previous week when Israeli commando forces boarded the Mavi Marmara, one of the vessels taking part in the flotilla.
The Nobel Women's Initiative travels to a troubled region of the world every two years to meet women's groups and highlight the difficulties they face.
The group last visited the Thai-Burma border and camps in east Chad holding refugees from Darfur in 2008.
It was established in 2006 by sister Nobel Peace Laureates American professor Jody Williams, Iranian doctor Shirin Ebadi, Kenyan professor Wangari Maathai, Guatemalan Rigoberta Menchu Tum and Ireland's Betty Williams and Mairead Maguire.