GAZA CITY, Gaza Strip (AP) — Israel destroyed the headquarters of Hamas’ prime minister and blasted a sprawling network of smuggling tunnels in the southern Gaza Strip on Saturday, broadening a blistering four-day-old offensive against the Islamic militant group even as diplomatic efforts to broker a cease-fire appeared to be gaining steam.

Hamas officials said a building used by Hamas for broadcasts was bombed and three people were injured. The injured were from Al Quds TV, a Lebanon-based television channel. The building is also used by foreign news outlets including Germany’s ARD, Kuwait TV and the Italian RAI and others.