JERUSALEM (AP) — The United Nations says that a program to reconstruct the Gaza Strip after this summer's 50-day war with Israel has begun.

Middle East peace process coordinator Robert Serry said the program started Monday with the sale of construction materials to 700 Gaza residents whose homes were damaged.

Palestinian estimates say that as much as $6 billion will be required to repair the damage sustained during the conflict.

It began after Hamas militants responded to Israeli arrests of Hamas activists in the West Bank by firing rockets at southern Israel.

Israel answered with a sustained aerial bombardment and ground invasion meant to stop the rocket fire and destroy a network of tunnels constructed to carry out attacks against it.

Serry some 60,000 Gaza residences need to be repaired immediately.