A deadly blast in central Cairo late Sunday, which was first blamed on a car crash, was actually caused by one of the cars in the crash, a vehicle packed with explosives and intended for use in a future terrorist attack elsewhere, Egyptian security forces said Monday.

At least 20 people were killed and 48 injured, three of them critically, according to the Egyptian Health Ministry.

The explosives-laden vehicle was being driven against traffic, the Interior Ministry said in a statement, when it crashed into three cars on the Nile Corniche in front of the National Cancer Institute, a major hospital. There was no explanation about why the car was being driven against traffic, other than that it was being driven somewhere else to be used in a future act of terrorism. No details as to where or when were given.