Activists have denounced Israel's unprecedented designation of six prominent Palestinian human rights groups as terrorist organizations.

Rights activists considered the move as a blatant attempt to prevent the groups from documenting rights abuses in the occupied territories, mainly by Israel, but also by the increasingly authoritarian Palestinian autonomy government in the occupied West Bank.

The Ramallah-based Bisan Center for Research and Development said in a statement that the Israel announcement to designate it, along with five other Palestinian Palestinian civil society organizations proves the criminal nature of Israeli occupation.

"We hope that the International community will put enough pressure on Israel so that it will back down," said Ubai Aboudi, head of the Bisan Center for Research and Development, one of the targeted groups.

Israel alleged that the six groups are a front for the Popular Front for the Liberation of Palestine, a small, secular, left-wing movement with both a political party and an armed faction that has carried out deadly attacks against Israelis.

Bisan and Al-Haq, the oldest of the Palestinian rights group, said they have not had contact with Israeli authorities since the decision was announced Friday. Bisan and Al-Haq denied having any links to the PFLP, which is considered a terrorist organization by Israel and Western countries.

The other four groups targeted by Israel include prisoner rights groups Addameer, Defense for Children International-Palestine, the Union of Palestinian Women's Committees, and the Union of Agricultural Work Committees. The majority of the organizations target human rights violations by Israel as well as the Palestinian Authority, both of which routinely detain Palestinian activists.

The initial international reaction has ranged from frosty to sharply critical.

The United States, Israel's closest ally, said it had not been given a warning about the decision and would seek more information. 

The UN Human Rights Office in the Occupied Palestinian Territory said Saturday that the reasons cited by Israel's defense minister were "vague or irrelevant," and denounced his decision as to the latest move in a "long stigmatizing campaign" against the organizations.

The European Union delegation to the Palestinian territories said past allegations of the misuse of EU funds by partners "have not been substantiated" but that it takes the matter seriously and is looking into it.