Four volunteers helping impoverished Palestinian farmers were caught up in an onslaught of tear gas and grenades.

The aid workers from the Brighton and Hove Palestine Solidarity Camp were based in a West Bank refugee camp when it was raided by Israeli forces.

The world's Press reported how the town of Tulkarem was invaded on Tuesday, in reprisal for the killing of five Israelis at a kibbutz last Sunday.

Israeli authorities said they were searching for a militant from Tulkarem affiliated to Palestinian leader Yasser Arafat's Fatah movement.

However, Chris Osmond, one of the Brighton volunteers, said Israeli forces had already occupied the area when the kibbutz killings took place.

He said: "We know because we were at the camp while it was being taken."

Mr Osmond, Zoe Mars, Laura Maritano and Trini Jesse had intended to spend most of their time helping farmers in the village of Falamia, near Tulkarem.

They wanted to bring in the olive harvests which Palestinian farmers feared were threatened by government restrictions and thefts by armed settlers.

They were stopped when Israeli military police told the farmers they had no right to harvest disputed land.

The aid workers asked the farmers if they wanted to organise a protest but were surprised when they declined and voluntarily handed the olives to police.

The police later promised to return the olives but had not done so by the time the Sussex team returned home.

The volunteers' duties shifted to providing medical help when they arrived at the 19,000-strong refugee camp on Friday last week.

The camp had been invaded the night before, with reports of five people being shot.

More Israeli troops arrived with tanks firing sound grenades and canisters of tear gas into crowded, residential areas.

Mr Osmond, 22, of Dudley Road, Hollingdean, said: "It was very unpleasant and frightening being caught up in it. The camp was under siege and lots of people were getting hurt."

Mr Osmond is a student at the University of Sussex, where Miss Maritano, 37, is teaching and studying for a PhD in social anthropology.

Mrs Mars is an administrator at the Institute of Development Studies, while Worthing-based Miss Jesse is a Spanish teacher.

The group will talk about their trip during a public meeting to be held at the Friends Meeting House in Ship Street, Brighton, today at 2.30pm.

Brighton MPs David Lepper and Des Turner will be among the guest speakers.