"It is very important for Boris Johnson as he enters 10 Downing Street to understand that Iran does not seek confrontation, that Iran wants normal relations based on mutual respect," Zarif told reporters in Managua, the capital of Nicaragua, AFP reported.
Zarif was responding to a question about whether he had a message for Johnson who would take over from Theresa May as prime minister on Wednesday.
Britain has demanded that Iran release a UK-flagged tanker seized in the Persian Gulf on Friday.
That came two weeks after British authorities impounded a tanker carrying Iranian oil off Gibraltar on suspicion of it breaching European Union sanctions against Syria.
Zarif said that move by Britain was orchestrated by the United States.
"It was clear from the very beginning that the United Kingdom was doing the bidding for the Trump administration," said Zarif.
"What the Brits did and what the Gibraltar authorities did in the Strait of Gibraltar was a violation of international law. It was piracy."
British Foreign Minister Jeremy Hunt said at the weekend that London wanted to "de-escalate" tensions with Iran but insisted that the Grace 1 tanker was seized because "it was carrying oil, against EU sanctions, to Syria."
Zarif described those allegations as "unfounded" and accused the British of acting "holier than the Pope" in applying rules the "EU itself would not do."
"Everybody understands that starting a conflict may be easy, but ending it would be impossible," he said.
Hunt told the British Parliament Monday he would seek to "put together a European-led maritime protection mission" for Persian Gulf shipping.