Israel and Jordan on Sunday barred pro-Palestinian US and European activists from trying to cross into the West Bank to deliver aid to students, a number of sources said.
Olivia Zemor, spokeswoman for the "Welcome to Palestine" group spearheading the mission, told AFP that one bus of activists was allowed through the Allenby Bridge border crossing by the Jordanian authorities but the Israelis turned them back.
"The (Israeli) authorities took all their passports and stamped 'entry denied' on all of them and told them to return," she said.
"The second bus was prevented (from crossing) by the Jordanians at the request of the Israeli authorities. They obeyed the orders of the Israelis," she said.
"One police officer told us that 'we got orders from Israel. We cannot let you leave'. We demanded explanation and nobody gave us any explanation. Then some of us demonstrated," she said.
An Israeli defence ministry official in Jerusalem confirmed that Israeli authorities had stopped the activists from entering the West Bank after a group of them arrived at the Allenby Bridge crossing.
"A small group of provocateurs, rioters and known troublemakers arrived at the Allenby crossing earlier today," the official said.
"The state of Israel exercised its right to refuse their entry, and they returned to Jordan."
Earlier Sunday, Walid Attalah, a spokesman for the "Welcome to Palestine" campaign in Jordan told AFP that the two buses had been prevented from crossing by the Jordanians.
"Two buses carrying 100 activists were not allowed to leave the Jordanian side" of Allenby Bridge Crossing, also known as King Hussein Bridge between the West Bank and Jordan, Attalah said.
Atallah said the "activists left the buses and started to demonstrate near the checkpoint. One of them fainted and was taken to hospital."
As part of the campaign, aimed at highlighting Israel's control over entry to the occupied territories, the activists sought to provide Palestinian students with a tonne of toys, pens, notebooks and other supplies.
"This is our fourth initiative to enter Palestine," Zemor told a news conference before leaving for the crossing, around 35 kilometres (20 miles) southeast of Amman.
"We have around 100 participants, from France, Belgium, Spain, Switzerland, the United States, aged between 10 and 50. All kinds of people, from all backgrounds and religions. They are all motivated to visit Palestine."
Five school buses drove the activists to the crossing as they chanted "Free Palestine!" and sang Palestinian traditional songs. Some wore T-shirts with "I have a dream" printed on them, while others flashed V-for-victory sign.
The campaigners tried to enter the occupied West Bank through Israel in July 2011 and April 2012, but the authorities at Tel Aviv's Ben Gurion airport denied them entry.
The activists, who had planned to stay for a week in the West Bank, say their mission comes at the invitation of Bethlehem governor Abdel-Fatah Hamayel.
Some activists had been sceptical in advance they would be allowed in.
"I tried in July last year and April, but the Israelis put me in prison for one day. I expect they will reject us again just like they did before. It is ridiculous and a shame," American volunteer Michael Rabb told AFP.