Bernardo Alvarez, the Venezuelan ambassador in Washington, said on Thursday: "We are - and we are going to be - a reliable source of oil for the world, including the United States."
Hugo Chavez, president of Venezuela, said on Saturday that he could shut his government's US-based refineries and sell oil to nations other than the United States if Washington decided to cut diplomatic ties.
Chavez said he did not want to take such measures after he expelled a US military attache on spying charges and Washington responded by ordering out a senior Venezuelan diplomat who was Alvarez's chief of staff.
Venezuela, the world's No 5 oil exporter, supplies about 15% of US petroleum imports.
Venezuelan state oil firm PDVSA also operates refineries and petrol stations in the United States through its Citgo refining and retailing arm.
Washington has made no suggestion that it plans to cut off relations with Venezuela, but the deteriorating ties sometimes disturb the world's oil markets.