The measure, taken on Sunday, is usually used against Palestinians and occasionally against ultra-nationalist Jews.

Tali Fahima, was arrested three weeks ago on suspicion of involvement in planning what police called "a terrorist attack" against Israelis.

Fahima, 29, who once offered herself as a human shield to protect a wanted Palestinian in the West Bank, denied the accusation.

"Defence Minister Shaul Mofaz adopted the recommendations of the Shin Bet and all of the security authorities and signed an administrative detention order against Tali Fahima," a ministry spokeswoman said.

She said the order would be in effect for six months.

A self-described former supporter of Prime Minister Ariel Sharon's right-wing Likud party, Fahima said she began to identify with the Palestinian struggle for statehood after befriending a Palestinian fighter in the West Bank city of Jenin.

Appeal

Fahima's lawyer told reporters the detention order showed the authorities had failed to gather sufficient evidence for an indictment and were persecuting her for her political beliefs.

She said she planned to appeal.

Figures provided by the Israeli human rights group B'Tselem, which monitors Israeli actions in the West Bank and Gaza Strip, show that Israel is holding some 730 Palestinians without trial.

Nine ultra-nationalists residing in illegal Jewish settlements in the West Bank and suspected of planning attacks against Palestinians, have also been detained without charge in recent years and released, B'Tselem said.