Gunshots have been fired in the Philippine senate as a senator who is wanted by the international criminal court (ICC) remained holed up in the building to evade arrest.

Ronald dela Rosa, a Philippine senator accused of crimes against humanity for his role in overseeing the former president Rodrigo Duterte’s “war on drugs”, has spent two nights in the country’s senate in a standoff with the authorities.

Late on Wednesday, after Dela Rosa claimed he faced imminent arrest, military personnel entered the senate building, some carrying assault rifles. Local media showed scenes of chaos, and the sound of gunfire later rung out.

It is unclear who fired the shots. The interior secretary, Jonvic Remulla, said the incident would be investigated. Referring to Dela Rosa by his nickname, he told media outside the building: “I will not arrest Senator Bato. I am here to secure everyone.”

“We do not know who is behind this,” Remulla said of the gunfire. “But we will find them.” He said there was security footage of the incident.