The Embassy Protection Collective activists have been camped out inside the embassy for weeks, at the invitation of Venezuelan diplomats, anticipating that the country's opposition movement headed by Juan Guaido will soon attempt to take over the property.
"Three people were arrested," the officer said.
The third person was a Venezuelan opposition supporter, the witnesses said.
Guaido's representatives in March seized control of two other buildings in Washington that belong to Venezuela's Defence Ministry, along with a consular property in New York.
The advocacy group Code Pink, whose members have joined the Collective, said in a statement on Twitter that Thursday's arrests occurred as two activists were trying to deliver food and medicine to the protesters inside after they had run out of supplies.
Code Pink said the activists were taken into the custody of the Secret Service. When contacted by Sputnik, the Secret Service did not immediately respond to a request for comment.
Code Pink later tweeted an update saying that authorities eventually allowed food, medicine and other supplies to be transported into the building. But the group questioned why its member, who they identified as Ariel Elyse Gold, had been arrested "trying to do just that."
Following Thursday's arrests, law enforcement officers at the scene erected metal barriers in front of the embassy, a Sputnik correspondent reported.
Tensions in Venezuela have been high since January, when Guaido proclaimed himself the interim president and was supported by the United States and its allies. Maduro, in its turn, was back by Russia and China, among other states, as the only legitimate president of Venezuela.