The International Solidarity Movement (ISM) told Aljazeera.net on Tuesday that farmers near Nablus had banked on an international presence to stop occupation troops preventing them from gathering their own crops.
But Israeli soldiers took the two Australians, German and British peace activists into custody at the illegal Ariel settlement and detained a further four farmers at the Alon More colony.
A British ISM volunteer, Siama Ahmad, witnessed all the arrests just outside the village of Salim.
She told Aljazeera.net that "Nick, George, Rihab and Frank did nothing other than ask Israeli soldiers why they were preventing farmers from their own land".
Ahmad added the crop is now likely to go to waste, as numerous able-bodied males have been taken into custody at one of the most important times in the farming calendar.
But an Israeli occupation forces official, Major General Moshe Kaplinski, said farmers were not yet permitted to work their own land given the unstable security situation.
In a statement published on the Israeli Defense Force website, however, Kaplinski said he will approve plans to permit Palestinians to gather their olive harvests as soon as relevant security measures are taken and after "reinforcement of forces in sensitive areas".
The official added that permits had been granted for an additional 1000 Palestinian workers, and the agricultural gates would be opened for longer hours to allow the entrance of Palestinian workers into the olive groves.