A one-ton bomb exploded beneath a security headquarters in southern Gaza on Wednesday, killing at least one person and nearly destroying the building, Palestinian security officials said. The bomb was hidden in a tunnel dug under the Preventive Security headquarters in the town of Khan Yunis, said Ali Qaisi, a presidential guard spokesman. Witnesses said that before the blast, Hamas militants called on the security officers inside the building to come out or they would blow up the place. Qaisi said he had reports that many were killed and injured, but security officers were still sifting through the rubble. Medics said at least one person was killed and eight others injured.