Tehran has dismissed Washington's threat of new sanctions as a desperate rerun of failed measures, even as it moves to formalise a regime of fees on Strait of Hormuz transit while the strategic waterway remains effectively closed to unauthorized oil tankers.

US Treasury Secretary Scott Bessent is due to hold a press conference Monday afternoon, where he is expected to announce new sanctions on Iran that he has described as the "toughest sanctions in history" against the Islamic Republic.

Iranian Foreign Minister Abbas Araqchi rejected the threatened measures on Sunday, saying they would fail to bring Tehran to heel just as previous sanctions have, according to Reuters. He framed the looming announcement as a rerun of failed tactics, arguing that Washington's pivot away from military action and back toward economic pressure exposed weakness rather than strength. Araqchi called for the US to engage Iran on more equal terms, saying Tehran has not been moved by blockades or military pressure and does not expect the latest measure to change that calculus.

The renewed pressure campaign arrives at a moment when Iran's economy is already strained by existing sanctions and by nearly six months of war, which began when the US and Israel launched strikes on the country in late February. Tehran has weathered intense US economic pressure before, including the "maximum pressure" campaign launched after Washington's 2018 withdrawal from the 2015 nuclear deal, which drove Iranian oil exports to multi-decade lows without halting them entirely.

Despite the toll, Tehran has held its position at the Strait of Hormuz, bringing tanker traffic through the vital oil corridor to a near standstill by refusing passage to unauthorized oil tankers. Hormuz is the world's most important oil chokepoint: roughly 21 miles wide at its narrowest point, it normally carries about a fifth of globally traded oil — some 20 million barrels a day — and about a fifth of the world's seaborne liquefied natural gas, most of it from Qatar. The strait remains effectively closed to vessels without Iran's authorisation, and that blockade has been a significant factor pushing global oil prices higher.

Enforcement is now being paired with monetisation. Iran's Persian Gulf Strait Authority has warned that ships violating its declared transit arrangements face fines, seizure or confiscation, and that vessels aiding blacklisted tankers through ship-to-ship transfers also face blacklisting themselves. Separately, Iran's parliamentary National Security and Foreign Policy Commission has approved Article 3 of a bill on the strait that would allow the state to charge fees on navigation, environmental, fueling, insurance and safety services for vessels passing through. The proposed charges would sit atop a long-standing legal baseline for the waterway, where commercial ships normally enjoy transit passage under the UN Convention on the Law of the Sea — a treaty Iran has signed but never ratified.

Taken together, the measures point to Tehran positioning itself as a formal gatekeeper of Hormuz traffic rather than simply obstructing it. The advance of the fee bill through parliament suggests Iran is moving toward formalised, monetised control of the waterway rather than a purely war-linked disruption, raising the odds that this becomes a semi-permanent cost layered onto Gulf shipping rather than something that unwinds once the conflict does.

For oil markets, the near standstill in Hormuz shipping keeps a geopolitical risk premium embedded in oil prices, with traders likely to stay cautious heading into Monday's announcement from Washington on new sanctions. Freight and insurance costs for tankers transiting the strait are likely to remain elevated regardless of how the sanctions decision lands.

President Trump has warned that any country offering Iran an economic "lifeline" will face consequences, a message aimed in part at China, which purchased more than 80 percent of Iran's exported oil in 2025, according to the analytics firm Kpler. Any sign that China, the largest buyer of Iranian crude, moves to comply with US pressure would be read as a potential supply-side shift, though Beijing's public preference for a diplomatic resolution points to limited near-term appetite to do so. Beijing has publicly called for the conflict to be resolved through diplomacy.

Pakistan has taken on a mediating role in the six-month conflict, and markets will watch its efforts for any sign of a diplomatic off-ramp that could ease the risk premium built into oil prices. Pakistan's army chief, Asim Munir, is due to visit Tehran as part of those mediation efforts, to discuss recent developments including the threatened new sanctions.

Iranian officials have offered mixed signals on the path forward. Parliament speaker Mohammad Baqer Qalibaf pointed to interest from neighbouring states in new regional security and economic arrangements, while accusing Washington of prioritising Israel's security over that of its own regional allies. President Masoud Pezeshkian, by contrast, has continued to call for a diplomatic solution to the standoff, arguing that Iran is negotiating from a position of strength rather than weakness.

Separately, a report published on Friday looks set to complicate any move toward an agreement between the two sides: Iran plans oil strikes to hurt Trump before midterms, official says.

With the new sanctions due on Monday, a transit fee regime advancing through the Iranian parliament, and Pakistan's mediation effort still in motion, the coming days are likely to determine whether economic pressure, formalised control of the strait, or diplomacy sets the terms of the next phase in the standoff between Tehran and Washington.