Israeli forces have shot and killed two Palestinians from the occupied West Bank during a confrontation, as Israel steps up its operation to find three missing teenagers.

The latest death on Sunday brings to four the number of confirmed fatalities since Israel started its operation to find the missing teens. Soldiers entered several Palestinian cities and villages in the occupied West Bank, rounding up six suspected armed men, the Israeli military said.

Israel has said its West Bank operation is twofold - to find Gil-Ad Shaer and US-Israeli national Naftali Fraenkel, both aged 16, and Eyal Yifrah, 19, who went missing near an Israeli settlement on June 13, and to deal a substantial blow to Hamas.

In an interview with Al Jazeera, Mark Regev, chief spokesman of Israeli Prime Minister Benjamin Netanyahu, said that his government is "organising a very vast operation" in the West Bank.

"We are doing everything that we can do" to find the missing teenagers," he said.   

Hamas has neither denied nor confirmed involvement in the disappearance of the youths.

Shortly after the Israeli troops withdrew, angry Palestinians reportedly attacked a police station, chanting against security coordination. The Palestinian Authority officers fired warning shots injuring two other Palestinians, witnesses told Al Jazeera.

Clashes also erupted in Ramallah, leaving at least 11 Palestinians wounded. 

'Collective punishment'

Before dawn, Israel carried out air strikes on four sites in the Hamas-ruled Gaza Strip after armed groups launched three rockets from the territory into Israel. No casualties were reported on either side.

On Saturday, Israel sent more troops into the occupied West Bank. Its military said it arrested 10 Palestinians and that about 1,350 sites in the West Bank had been searched so far and more than 330 Palestinians detained.

Palestinian President Mahmoud Abbas has condemned the kidnapping but said the Israeli military sweep amount to collective punishment.

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An Israeli military spokeswoman said the soldiers found "electronic devices and magnetic media used for terrorism" that she said belonged to Hamas, without going into further detail.

Israel has also targeted welfare organisations it accuses of aiding Hamas. Soldiers raided 30 such institutions on Thursday and 15 more on Saturday, a military spokesman said.

Campaign group the Palestinian Prisoners Club said the army had arrested 37 people on Saturday.

Source: Al Jazeera and agencies