An Israeli study says Hamas, the militant group that controls Gaza, is engaged in the broadest and most significant military buildup in its history with help from Syria and Iran. It adds that Hamas is restructuring more hierarchically and using more and more powerful weapons, especially longer-range rockets against Israel's southern communities.

The study, by an independent research group with close ties to the Israeli military establishment, says that though the buildup will take some years to complete, it is in an intensive phase that has already led to better infiltration into Israel and a rise in the breadth and precision of rocket fire...