The number of Palestinians forced to provide information before being let out of Gaza for medical treatment is rising, an Israeli group has reported.

In the first three months of 2009 more than 400 patients were interrogated, Physicians for Human Rights says.

They say Israeli security services are involved in a systematic attempt to recruit Palestinians as collaborators.

Israeli officials say they are carrying out security checks to ensure those entering Israel do not commit attacks.

Spokesman Mark Regev told the AFP news agency that 13,000 Palestinians are treated in Israel each year.

However, Physicians for Human Rights says Israel also interrogated children, detained patients for undisclosed periods of time, and intimidated them during interrogations.

Those who did not co-operate were refused permission to leave Gaza for treatment, the group says.

Complicates process

Between January 2008 and March 2009 at least 438 patients were summoned for interrogations at Erez Crossing, the main crossing point for people between Israel and Gaza, the group says.

The data collected by the group has been presented to the Geneva-based UN Committee Against Torture.

"The data points to an increase in the ratio of the number of interrogations to the total number of applications submitted to the authorities at Erez Crossing," the organisation says.

The process of referring Palestinians in Gaza for medical treatment in Israel, or further afield, is a complicated one.

It was administered by the Palestinian Authority even after Fatah, the faction led by Palestinian Authority President Mahmoud Abbas, was ousted from Gaza in June 2007.

Earlier this year the World Health Organisation warned that the feud between Hamas and the Palestinian Authority was putting at risk the lives of critically-ill Gazans.

This followed the takeover by Hamas officials of the office that ran the referrals process in Gaza.

Because Israel refuses to deal with Hamas, which it considers a terrorist group, this effectively closed down the referrals process.

Hamas officials have long maintained that the process is inefficient and corrupt.