Israeli soldiers have shot and killed two Palestinians, including an 11-year-old boy, as troops tightened the closure around two cities in the West Bank.

The Palestinians were killed in Jenin, one of two Palestinian cities where the Israeli army has reinforced its positions in response to a series of terrorist attacks. Witnesses say the boy was shot while throwing stones at soldiers.

Israeli military sources say troops have re-occupied Palestinian-controlled territory around Jenin, and also tightened the closure on Nablus. The military says six of the seven Israelis killed in attacks this week were slain by militants from the Jenin area.

Palestinians call the incursions a violation of their territorial rights granted under various interim peace accords.

Israeli special forces arrested several members of the Palestinian intelligence services in a village near the West Bank town of Hebron. Earlier, several members of the militant group Islamic Jihad were also arrested in Hebron.

A brief gunfight erupted on Saturday in the Gaza Strip between Palestinian police forces and members of the Islamic Jihad movement. In a rare display of internal dissent, the clash occurred when police arrived at the home of Islamic Jihad official Mohammed al-Hindi to arrest him. A firefight broke out between police and Mr. al-Hindi's bodyguards. Mr. al-Hindi escaped without being arrested. No injuries were reported.

Palestinian President Yasser Arafat has been urged to arrest militants responsible for attacks on Israelis, but Mr. Arafat is under domestic pressure not to crack down on groups fighting in the 14-month-old uprising against Israeli occupation.

On Saturday, US envoy Anthony Zinni toured the Gaza Strip, meeting with Palestinian officials and observing areas shelled and bombed by the Israeli military.

The retired Marine Corps general is trying to persuade Israel and the Palestinians to implement a cease-fire and a plan designed to permanently end the violence proposed by an international commission led by former US Senator George Mitchell.

Israeli Prime Minister Ariel Sharon is in the United States preparing for meetings with President Bush and other top officials early next week.

The discussions are expected to focus on the conflict in the Middle East and the international war on terrorism.