According to Al Jazeera:
Officials from PalTel, which operates Internet and phone networks in Gaza, told Al Jazeera that Israeli bulldozers cut the cables at Nahal Oz two weeks ago, forcing the company to use another set of communications lines at the Erez crossing, which were then cut on Tuesday.
PalTel needed permits to repair the lines but had not yet received them from Israel, chief executive officer Ammar al-Aker said.
Follow the developments also at Twitter (I would not have realized without it). Also Sleepless in Gaza considers that this incident implies a risk of outright Zionist attack.