The bomb, planted near the toilets at the Zif school, south of Hebron, detonated as the children took a break from their lessons.

The children were evacuated from the school

The school headmaster and Israeli military sources have suggested that the bombs were planted by Israeli militants.

"We are checking to see... whether a Palestinian source, a criminal source or a Jewish source (was responsible)," police spokesman Gil Kleiman said.

In March, a Jewish vigilante group claimed responsibility for a bomb explosion at a Palestinian school near Jerusalem which injured five people.

Tense city

Hebron, home to 120,000 Palestinians and 400 Jewish settlers, is a tense city that is often the scene of violence.

Control of 80% of the city was handed over to the Palestinian Authority in 1997.

The remaining 20% is held by Israeli troops deployed to protect the highly committed settler community living in the heart of Hebron's old city.

The area under Israeli control is home to about 30,000 Palestinians who often live under strict military curfews.

Ongoing operations

The explosion comes in a period of decreased violence in the region.

However, Israel continues to carry out almost nightly raids on the Gaza strip, searching for suspected militants and alleged bomb and weapons workshops.

On Tuesday, the army carried out a sweep of an area near the Khan Younis refugee camp.

In a statement it said it had arrested 23 Palestinians "suspected of hostile activities against Israel" and destroying nine weapons factories.

Palestinians said the workshops were for domestic and farm use and were unrelated to militant activities.