A huge blast late Tuesday night rocked a training base run by Hamas in southern Gaza, and at least five people were hurt, witnesses and a health official said. Ambulances raced to the scene of the blast, on the site of an evacuated Jewish settlement next to the southern Gaza city of Khan Younis. The explosion could be heard all over the city. It was not immediately known what caused the blast. Hamas had no comment, and the IDF said it had no knowledge of the incident. Dr. Moaiya Hassanain of the Palestinian Health Ministry said two of the five wounded were in critical condition. He said all five were Hamas men. Witnesses said the blast destroyed the base, and a fire was burning there an hour afterward. They said a second, smaller blast was heard about 15 minutes after the first one. Hamas gunmen kept reporters away from the scene.