KHAN YOUNIS, Gaza Strip — Internet and telephone services collapsed across the Gaza Strip on Thursday for lack of fuel, the main Palestinian provider said, bringing a potentially long-term communications blackout even as Israel signaled its offensive could next target the south of the territory, where most of the population has taken refuge.

       Meanwhile, Israeli troops for a second day searched Shifa Hospital in the north for traces of Hamas. They displayed guns they say were found hidden in one building, but have yet to release any evidence of the central Hamas command center that Israel has said is concealed beneath the complex. Hamas and staff at the hospital, Gaza’s largest, deny the allegations.

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       The communications breakdown threatens to worsen the severe humanitarian crisis in southern Gaza, where Israeli airstrikes continue. Food, water and electricity are increasingly scarce, and the U.N. is struggling with fuel shortages of its own to deliver aid and help hospitals keep operating.