Police are investigating reports of some kind of sexual incident in East Boston Friday night, spokesman David Estrada said. The incident, which was labeled by police as “sexual in nature,” occurred on Chelsea Street at 8:30 p.m., Estrada said. Friday’s report follows reports of three woman sexually assaulted on Trenton and Chelsea streets Monday. The women described the attacker as a highly intoxicated man dressed in black. Police said The incident Friday night does not appear to be linked to Monday’s attacks. No other details were immediately available.