Women protesters said they were beaten, given electric shocks, subjected to strip searches while being photographed by male soldiers, then forced to submit to "virginity checks" and threatened with prostitution charges, Amnesty said.

"The Egyptian authorities must halt the shocking and degrading treatment of women protesters," the rights group demanded.

"All security and army forces must be clearly instructed that torture and other ill-treatment, including forced 'virginity tests', will no longer be tolerated, and will be fully investigated.

"Those found responsible for such acts must be brought to justice and the courageous women who denounced such abuses be protected from reprisals."

Amnesty condemned forced virginity tests as "utterly unacceptable" and intended to "degrade women".

"Women and girls must be able to express their views on the future of Egypt and protest against the government without being detained, tortured, or subjected to profoundly degrading and discriminatory treatment," it said.

Amnesty said the 18 women were initially taken to a Cairo Museum annex where they were reportedly handcuffed, beaten with sticks and hoses, given electric shocks in the chest and legs, and called "prostitutes".

Earlier this month, US Secretary of State Hillary Clinton warned that women were being shut out of political life in the aftermath of democracy revolutions in Egypt and Tunisia.

"In Egypt, the women who marched for freedom in Tahrir Square are now shut out of the committees and the councils deciding the shape of Egypt's new democracy," Clinton said.

"The Constitutional Committee has not a single woman member," she said.