Israeli forces have raided the normally quiet town of Jericho in the West Bank, seizing arms and arresting 20 people.
Witnesses said tanks and armoured personnel carriers moved in as helicopter gunships hovered overhead.
Palestinian cabinet minister Saeb Erekat described the operation in the normally quiet town as “a dangerous escalation by Israel”.
In the Gaza Strip, Palestinians said a nine-year-old boy was killed in a new incursion by Israeli forces.
“We have arrested more than 20 wanted men so far, among them senior people, and found weaponry that includes rifles and grenades,” an Israeli a military spokeswoman said about the Jericho operation.
Palestinian security sources said three of those arrested had been injured.
They also said that the house of a wanted man from the Fatah organisation was blown up.
The ancient town of Jericho has been one of the more peaceful areas of the West Bank, largely untouched by the violence of the last four years.
In Nablus, also in the West Bank, residents said Israeli troops were searching houses for militants.
In Rafah in the Gaza Strip, nine-year-old Omar Mohammed Abu Zreihan was killed after fighting broke out during an Israeli incursion, witnesses said.
Israeli armoured vehicles were destroying houses when Palestinian militants opened fire, they said.
According to hospital officials, the boy died when tanks fired toward houses in the area.
A spokesman for the militant group Hamas said one of its members was also killed in the northern Gaza Strip, at Beit Hanoun.
Ismail Nabhan, 26, was killed during a clash between gunmen and Israeli forces who had entered the area following a series of rocket attacks that hit Israeli territory.