By Jim Fish The BBC's correspondent in Jerusalem

Israel has rejected allegations that its security services have used torture to interrogate the leading Palestinian activist, Marwan Barghouti.

Lawyers for Mr Barghouti say that he has undergone physical and psychological maltreatment amounting to torture since he was arrested in the West Bank in April.

Lawyers for Mr Barghouti say he has been subjected to systematic sleep deprivation since his arrest in April

Mr Barghouti is one of the most prominent Palestinians ever held by the Israeli authorities.

As the leader of Yasser Arafat's Fatah faction in the West Bank, Mr Barghouti is also considered by Israel as the mastermind of a series of suicide attacks since the outbreak of the Palestinian uprising - the intifada - nearly two years ago.

'Tied to chair'

Lawyers for Mr Barghouti say he has been subjected to systematic sleep deprivation since his arrest in April.

They say that during long interrogation sessions he has been shackled to a chair by his hands and legs for hours at a time.

His lawyers say that although his spirits remain high, he has lost weight and appears exhausted.

This treatment, they say, amounts to torture and has been banned by the Israeli High Court since 1999.

Tip of the iceberg?

An Israeli Government spokesman denied categorically to the BBC that any such methods had been used against Mr Barghouti by the security service, Shin Beth.

The spokesman said they had strictly followed the precise guidelines for the treatment of detainees.

Sources close to the authorities say that precisely because Mr Barghouti is such a high-profile detainee, they have had to be especially cautious in their treatment of him.

If so, human rights activists suspect that the handling of less prominent prisoners - for example, suspected bombers - almost certainly amounts to torture.

One human rights monitoring organisation in Jerusalem says it has documented more than 300 such cases since the beginning of the intifada.