Britain said Thursday that Iranian vessels tried to "impede the passage" of a British oil tanker through the Strait of Hormuz.
A government statement said three Iranian vessels were involved with the incident, and that they backed off when they received a warning from a British warship.
Iran's Revolutionary Guards denied Britain's accusation. A statement carried by the semi-official Fars news agency said Guards patrol boats carried out normal duties and had "no clashes with alien boats, especially English boats."
Iranian President Hassan Rouhani had warned Wednesday that Britain would face unspecified "consequences" over the seizure last week of an Iranian oil tanker suspected of transporting oil to Syria in violation of sanctions.
Revolutionary Guards Deputy Commander Rear-Admiral Ali Fadavi described the seizure as an act of "stupidity ...a trait the American president has in spades and the British to some extent."
Tensions in the Persian Gulf have escalated between Iran and the United States and its allies since Washington stepped up economic sanctions against Tehran and moved to halt its oil exports as a part of a "maximum pressure" policy to force Iran to end actions deemed to undermine regional security.
Tensions began to heighten in May 2018 when U.S. President Donald Trump withdrew from a 2015 agreement with Iran and a group of world powers to contain Tehran's nuclear program. In response, Iran recently exceeded uranium enrichment limits in violation of the agreement.
British Defense Minister Penny Mordaunt said Britain is concerned about Thursday's disputed incident and urged Iran to "desecalate the situation."
China and Russia, both signatories to the Iran nuclear deal, also called for restraint.
The U.S. Central Command said "Threats to international freedom of navigation require an international solution. The world economy depends on the free flow of commerce, and it is incumbent on all nations to protect and preserve this lynchpin of global prosperity."
The Strait of Hormuz is a strategic waterway through which much of the oil in the Middle East is transported.