Iran is planning to charge foreign ships a toll in exchange for "protection" across the Strait of Hormuz, a key trade route and a flashpoint in the escalating dispute between the United States and the Islamic Republic.

A member of the Iranian Parliament's presidium said foreign commercial entities should compensate Iran as "the true provider of security in the region and international waters," according to the state-run Tasnim News Agency. Amirhossein Qazizadeh Hashemi claimed ships enter Iranian waters on their way through the strait and should therefore pay a toll.

That assertion doesn't jibe with clearly defined international agreements, former Navy officer Thomas Callender says.

"There's no question whatsoever about the rights of commercial vessels and tankers transiting the Strait of Hormuz and that they have this right to transit unimpeded," Callender, a senior fellow for defense programs at the Heritage Foundation, told the Washington Examiner.

"To be trying to charge essentially tax to pass through this is a form of extortion."

The Strait of Hormuz is a narrow, 21-mile waterway linking the Persian Gulf to the Gulf of Oman and greater Arabian Sea. About 18.5 million barrels of oil travel through the strait each day, accounting for 30% of the world's sea-traded oil. The waterway is considered crucial to global trade, but with a shipping lane only three miles long, it is also extremely vulnerable.

"It's kind of like the old movies where you'd see the mafia come in and bang up someone's store and say, 'Look, you want protection from someone banging up your store, you have to pay us,'" Callender said. "It's like an Iranian mafia requesting protection money from the commercial shipping industry and oil companies through the gulf."

The Iranian economy relies heavily on the oil trade, making it a ripe target for U.S. and international sanctions. The Trump administration has focused on Iranian oil as part of its maximum pressure campaign against the regime and warned allies to steer clear of doing business with Tehran.

In Gibraltar on Sunday, British Royal Marines seized and impounded an Iranian tanker, suspecting it of carrying oil to Syria, a violation of European Union sanctions. Iran is a close ally of Syrian President Bashar Assad, propping up his authoritarian regime as it continues to battle rebel groups. An Iranian Revolutionary Guards Corps commander threatened to seize a British ship in response, and the country's defense minister condemned Britain on Monday.

"These days we witnessed a threatening act from the government of England in the Strait of Gibraltar against a tanker from the Islamic Republic of Iran," Amir Hatami said. "This is an incorrect and wrong action, an action similar to maritime robbery ... certainly these kind of robberies will not be tolerated."

Iranian officials denied that the ship was on its way to Syria, though they have not specified its destination.

While the United States has long maintained a significant military presence in the Persian Gulf, it has grown in recent months as tensions with Iran continue to flare. In addition to a contingent of bombers, Patriot missile systems, and troops, the Pentagon sent the USS Abraham Lincoln strike group to the region recently.