An explosion destroyed a building inside a Palestinian national security compound in the northern Gaza Strip on Tuesday, killing two police officers and wounding seven others, Palestinian security officials said. The building was used as a collection point for unexploded Israeli shells fired into the northern Gaza Strip. The shells were later sent to another location to be disabled. The IDF denied any involvement in the explosion. Israel has been firing shells into northern Gaza in recent weeks in response to Palestinian rocket fire at Israel. The cause of the blast, which collapsed a one-floor building inside the compound in the town of Jebaliya, was not immediately known, according to Palestinian security sources. Mosud Salem, a security officer, said he was leaving the compound "when suddenly a big explosion shook the area and a big cloud of white smoke shot up." "I heard the sound of screaming. Some of our police where in that section of the building. We don't know what happened, everything happened so quickly. The explosion was so loud and everything collapsed in less than a second," he said. The blast killed at least two people, and rescue workers, using bulldozers to dig through the rubble, were searching for a third missing person, rescue officials said.