NEW BEDFORD — Four people are arrested following an investigation by New Bedford Police Narcotics Detectives into street level drug sales in the city's North End on Monday.

Complaints of drug activity led police to the area of Hope and Tinkham Streets, where they observed a drug transaction in progress in a vehicle at about 12:08 p.m. As part of the transaction, police seized 2.75 grams of heroin.

Police arrested both the seller, 43-year-old Paul David Lopes of Hope Street, and the buyer, 48-year-old Thomas Lopes of Armsby Street. Paul Lopes is charged with distribution of a Class A drug (heroin) and conspiracy to violate drug laws. Thomas Lopes is charged with possession of a Class A drug (heroin), as well as conspiracy to violate drug laws.

Then, less than an hour later, undercover officers observed another drug transaction in the area of 229 Sawyer Street at approximately 1 p.m. Police discovered a plastic bag containing fentanyl, and two syringes containing heroin.

Arrested was 41-year-old Matthew Vieira of Mattapoisett and 33-year-old Michael DeSouza of South Dartmouth, both on charges of possession of a Class B substance.