At least 14 people have been killed and 120 others injured after a car bomb exploded at a police building in the Nile Delta city of Mansoura, Egypt's Ministry of Interior said.

The explosion took place at 1:10 a.m. local time Tuesday at Dakhalya security headquarters in Mansoura, causing the collapse of parts of the five-floor building. Mansoura, the capital of the governorate of Dakhalya, is about 84 miles northeast of Cairo.

Five high-ranking police officers were among those to die in the blast. The head of security for Dakhalya, Sami el Mihi, was wounded in the blast, and two of his aides were killed, security sources told AFP.

The bombing comes weeks before Egypt is to hold a referendum on a new constitution that is billed by the country's military-installed authorities as the first step toward democratic rule after the army ousted President Mohamed Morsi in July.