Britain's detention of an Iranian oil tanker near Gibraltar last week "will not remain unanswered," Iran's chief of staff General Mohammad Baqeri was quoted by the semi-official Tasnim news agency as saying on Tuesday.
"The seizure of the Iranian oil tanker based on fabricated arguments will not remain unanswered, and if necessary Tehran will respond appropriately," Baqeri said.
The British Royal Marines advanced to the Grace 1 ship off the coast of Gibraltar on Thursday and detained it on charges of violating EU sanctions by transferring oil to Syria.
Subsequently, Iran summoned the British ambassador in Tehran for what the Iranian Foreign Ministry described as the "illegal detention" of the oil tanker.
Iran demanded the immediate release of the tanker, while a commander in Iran's Revolutionary Guards on Friday threatened to detain a British ship in response.