Global Jihad operatives in the Gaza Strip and Sinai.

The attack took place while the Egyptians were breaking the daily Ramadan fast. Two armed groups whose members are identified with Al-Qaida raided the post, a few kilometers from Kibbutz Kerem Shalom, in two off-road vehicles.
They fired RPG rockets and machine guns at the position, one of the Egyptian army's key posts on the border. There were an estimated 20 soldiers at the post at the time of the attack. It is believed the attackers killed approximately 15 soldiers and abducted the others.

Israel as a secondary goal:

 Sunday's attack was unusual in its daring. It is clear that the group that carried it out wanted first and foremost to cause mass casualties among Egyptian soldiers, and apparently, to deter soldiers from serving in the area. Striking Israel was apparently a secondary goal.

Sinai attack proves Islamist terrorists are targeting Egyptians as well as Israelis - Israel News | Haaretz Daily Newspaper