HONG KONG — The Chinese authorities, facing enormous pressure to account for catastrophic chemical blasts that killed more than 100 people two weeks ago, said Thursday that they had detained or placed under investigation 23 people in connection with the disaster.

Those being investigated included the chief of the transportation department in Tianjin, the northeastern city where the blasts erupted on Aug. 12. Among those detained were employees of the company that owned the warehouse that was at the epicenter of the explosion and employees of the company that conducted the safety assessment of the warehouse.

The authorities described the detainees as directly responsible for the blasts in Tianjin, according to a report by Xinhua, a state-run news agency. The explosions killed 139 people and injured at least 700.