Lutfi Abu Oun, mayor of the village of Jaba'a, said two of the teenagers were seriously hurt and all of the wounded were taken to hospitals in the West Bank cities of Jenin and Nablus.

School headmaster Ismail Salah said the explosion tore through a classroom for 16-year-old boys just as they returned from a midday recess.

Desks and chairs were thrown about and splintered, and pools of blood and glass shards littered the floor, witnesses said.

An unknown Jewish group calling itself "Revenge of the Infants" claimed responsibility for the blast in a message sent to Israeli reporters' pagers, police said.

"We have no hard evidence whether this was a true announcement," Israeli police spokesman Gil Kleiman said. "We have opened an inquiry and a decision has to be made whether we can send a bomb squad to investigate."

Jewish vigilantes have carried out several attacks against Palestinians during the 30-month-old Palestinian uprising for independence, in which militants have mounted dozens of bombings and shooting assaults on Israelis.

Jaba'a was part of the West Bank territories handed over to Palestinian rule under interim peace accords in the 1990s.

Israel's army has reoccupied much of the West Bank since a wave of Palestinian suicide bombings in Israel last summer.

 http://reuters.com/newsArticle.jhtml?type=worldNews&storyID=2534910