RAMALLAH, Feb 27 (Reuters) - A Palestinian woman, released by Israel in a prisoner swap last year but re-arrested earlier this month and held without charge, is on a hunger strike to protest at her treatment, officials said on Monday.

Hana Shalabi started refusing to eat 12 days ago, her lawyer and a Palestinian prisoners's organisation said, becoming the second Palestinian detainee to go on a hunger strike in quick succession.

Israel struck a deal last week with Khader Adnan, who is a member of the militant Islamic Jihad movement, persuading him to end his 66-day fast after assuring him that he would be released in April from his detention without trial.

Shalabi, 30, is also a member of Islamic Jihad, which is committed to Israel's destruction.

She was seized from her home in the occupied West Bank on Feb. 16 and has complained of repeated mistreatment. Her lawyer said she has been put in solitary confinement as punishment for the hunger strike.

"She told me that she was beaten in front of her family at the time of her arrest, in prison during interrogation and again when she refused to succumb to a full body search by male soldiers," lawyer Fawaz Shaloudi told Reuters.

A spokeswoman for Israel's Prisons Service, disputing the allegations, said Shalabi had been on hunger strike for only eight days.

"The isolation was part of routine procedure to deal with hunger strikers and she was put in a cell on her own, but it was not solitary confinement punishment. Today she was returned to a cell with another inmate," spokeswoman Sivan Weizman said.

"There has been no mistreatment in prison. She was not searched by a male prison guard and she is getting visits. Indeed, she has not complained of mistreatment while in the custody of the Prisons Service," Weizman added.

Shalabi was held by Israel for 25 months under so-called administrative detention before she was released last October as part of a prisoner swap in which some 1,000 Palestinians were freed in exchange for Israeli soldier Gilad Shalit, who was held incommunicado by militants in Gaza for five years.

Israeli human rights groups have condemned detention without trial. Israeli authorities say the procedure is used in some security-related cases and helps to protect confidential sources from exposure in court.

Qaddoura Fares, the chairman of the main Palestinian prisoners's organisation, said 310 Palestinians are in administrative detention. He said that since the Shalit deal, 15 Palestinians have been rearrested and six are still in jail.