NABLUS, West Bank,(Reuters) – Israeli soldiers shot dead a Palestinian on Thursday in the West Bank city of Nablus, the fourth they have killed in a five-day-old operation against militants, Palestinian medics said.

The operation is the army’s biggest in the occupied West Bank since the militant Hamas group won a Palestinian election on Jan. 25.

Medics said soldiers shot dead an 18-year-old and wounded five other Palestinians while dispersing stone throwers in the centre of Nablus. The Israeli army said troops fired at Palestinians who either shot at them or threw fire bombs.

The Israeli gunfire hit at least three Palestinians, the army added.

Witnesses said the violence erupted after the army expanded the scope of the operation from Balata refugee camp, on the outskirts of Nablus, into the city centre, blocking main roads and forcing schools and some businesses to close.

An Israeli military official in Jerusalem said troops were searching the Nablus area for militants suspected of involvement in planning suicide bombings and other attacks. The official did not say how long the operation would last.

The main targets of the raid have been Islamic Jihad, which carried out two suicide bombings in Israel in recent months, and al-Aqsa Martyrs Brigades, a militant group that is part of the mainstream Fatah movement.

More than two dozen militants have been arrested in the Nablus area and elsewhere in the West Bank since the operation began on Saturday, Israeli military sources said.

Palestinians said more than 50 people had been shot and injured by the army during confrontations, some by live ammunition and others by rubber-coated metal bullets.

In Gaza, Islamic Jihad militants said they fired seven rockets at Israel in response to the Nablus operation, in which a senior commander in the group was killed on Tuesday. The army said five rockets struck in Israel, causing no casualties.