Muhammad Abu Barka, 18, was shot in the chest by Israeli snipers on Thursday, Aljazeera.net correspondent Laila El-Haddad reports.
The snipers were nested in the Abu Uraif area near the illegal Israeli settlement of Kfar Darom. Barka died of his wounds in the Shuhada al-Aqsa hospital, according to Palestinian medical sources.
Two others, Ahmad Abu Shawish, 19, and Muhammad Abu Musabih, 15, were fatally wounded when Israeli soldiers opened fire on a group of stone-throwing youths and died soon afterwards.
Earlier on Thursday, Muhammad Jamal Barakeh, 19, was reportedly killed in similar circumstances.
An Israeli army spokesperson told Aljazeera.net the deaths were "still under investigation".
He said the raid began after a 10 metre deep by 400 metre long tunnel was discovered under the settlement early this morning. Israeli forces are attempting to trace the origin of the tunnel, he said.
Israeli forces withdrew from the al-Namsawi quarter, west of the Khan Yunus refugee camp in northern Gaza after partially dynamiting a five-storey building, our correspondent reported.
The explosion displaced hundreds of Palestinians and destroyed the headquarters of the National Security agency, the correspondent said.
Gaza correspondent Laila El-Haddad contributed to this report