Israeli forces say they have arrested one of the most wanted leaders of the Islamic militant organisation Hamas.

The man, Jamal Abu al-Hayja, is suspected of involvement in several suicide attacks.

He was held during house-to-house searches after a big Israeli incursion into a Palestinian refugee camp in the West Bank town of Jenin.

The Israeli army has been positioned there as part of an operation in most West Bank towns that began two months ago with the aim of stopping suicide attacks.

How can you expect a complete change in the situation in two days after a conflict running almost two years?

Binyamin Ben-Eliezer Israeli defence minister

Shots were exchanged as tanks entered the camp with helicopter support. One Israeli soldier was lightly wounded.

Mr al-Hayja, who lost an arm in clashes with Israeli troops early in the year, had been hiding in Jenin or nearby villages since Israel's massive spring incursion into the West Bank.

Palestinian sources said Islam Jarrah, an aide to the militant leader, and large numbers of others were also arrested.

Israeli Defence Minister Binyamin Ben-Eliezer said the operation did not mean that last week's security agreement with the Palestinians had been suspended.

"It is not dead. It lives," he said. "How can you expect a complete change in the situation in two days after a conflict running [almost] two years? I expect efforts from them."

Under the deal, Israel was to scale down its military presence in some Palestinian areas in return for tougher action to stop suicide bombings.

Israeli troops have already pulled out of Bethlehem, but the Palestinians have accused them of delaying a planned withdrawal from Hebron.

Clashes and arrests were also reported in Hebron, Nablus and Ramallah.

And Israeli military sources said that two mortar shells were fired at Jewish settlements in the south of the Gaza Strip, but no-one was injured.

Explosive devices

The Israeli army has meanwhile restricted the sale of certain chemicals in the West Bank, saying they could be used to make home-made explosives.

This measure was taken because terrorist organisations utilise chemical materials to prepare explosive devices

The Israeli army

The entry and sale of urea, nitric acid, sulphuric acid and potassium nitrate will all be subject to the new regulations.

Palestinians who want to buy the chemicals listed, for both commercial and private purposes, will now need a permit from the Israeli military. Without permission, the army will confiscate the chemicals.

The chemicals are routinely used in fertilisers, and the Palestinian Authority has told the BBC that the restrictions will damage fruit and vegetable production and affect the winter olive harvest in the West Bank.

A statement from the Israeli army said the move was part of "the war against terrorist infrastructure".

The measure is part of a series of Israeli moves designed to prevent attacks against Israel. Over the last few months these have included extensive military curfews, travel bans and the demolition of suicide bombers' homes.

Palestinian militant groups like Hamas and Islamic Jihad have wreaked havoc in Israel since the intifada began more than a year-and-a-half ago, launching repeated suicide attacks on Israeli targets.