Britain's seizure of an Iranian oil tanker off Gibraltar was illegal and will be detrimental for Britain, Iran's President Hassan Rouhani said on Sunday, according to the official presidency website.

British forces captured an Iranian oil tanker in early July near Gibraltar, accused of violating sanctions on Syria. On July 19, Iranian commandos seized a British-flagged tanker in the Strait of Hormuz, the world's most important waterway for oil shipments.

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Abbas Araqchi, a senior member of the team who negotiated the deal and a deputy foreign minister also said on Sunday that Britain's seizure of an Iranian oil tanker in Gibraltar is a violation of the 2015 nuclear deal, according to the ISNA news agency.

"We witnessed the seizure of an oil tanker carrying Iranian oil in the Strait of Gibraltar which in our view is a violation of (the nuclear deal)," Araqchi said. "And the countries who are part of (the nuclear deal) shouldn't create obstacles for the export of Iranian oil."

Britain said on Monday it was planning a European-led force to escort tankers through the world's busiest oil shipping lane in response to Iran's seizure of a UK-flagged vessel on July 19.

Iran slammed the proposal as "provocative," according to the government spokesman Ali Rabiei, "We heard that they intend to send a European fleet to the Persian Gulf which naturally carries a hostile message, is provocative and will increase tensions," he said on Sunday.

"We are the biggest agent of maritime security in the Persian Gulf," Rabiei said, adding that Iran believed the security of the oil-rich Gulf had to be maintained by countries in the region.

Rouhani said such a force would only make matters worse. "The presence of foreign forces will not help the region's security and will be the main source of tensions," Rouhani said after talks in Tehran with Oman's minister of state for foreign affairs, Yusuf bin Alawi.

Britain on Thursday ordered its navy to escort UK-flagged ships through the Strait of Hormuz, where the Stena Impero was seized by Iran's Islamic Revolutionary Guard Corps.

But it has so far only received a cool response from the continent to its proposal for a multinational escort fleet that would exclude the United States.

France said on Thursday it was not willing to send extra military assets to the Gulf, but would share information and coordinate its currently deployed assets. The US military has said it is already monitoring the strait and developing a "multinational maritime effort" dubbed Operation Sentinel to increase surveillance and security in key Middle East waterways.

Rouhani blamed Washington for sparking the crisis when it pulled out of the 2015 nuclear deal known by its formal name Joint Comprehensive Plan of Action (JCPOA).

"The unfortunate incidents and tensions in the region today have their roots in the unilateral U.S. withdrawal from the JCPOA agreement and the delusions of the country's administration," said the Iranian president.

"Iran will strongly stand against any wrongdoing and illegal activity that would threaten maritime security in the Persian Gulf, Strait of Hormuz and the Sea of Oman," he was quoted as saying by ISNA.

(With inputs from Reuters, AFP)

(Cover: The UK-flagged oil tanker, Stena Impero, is seized by the Iranian Revolutionary Guard as it passes through the Strait of Hormuz, July 19, 2019. /VCG Photo)