Iran has arrested more than two dozen people, including senior intelligence officers, military officials and staff workers at a military-run guesthouse in Tehran, in response to a huge and humiliating security breach that enabled the assassination of a top leader of Hamas, according to two Iranians familiar with the investigation.

The high-level arrests came after the killing in an explosion early on Wednesday of Ismail Haniyeh, who had led Hamas’ political office in Qatar and was visiting Tehran for the inauguration of Iran’s new president and staying at the guesthouse in northern Tehran, Iran’s capital.