United States military forces boarded an oil tanker previously sanctioned for smuggling Iranian crude oil in the Indian Ocean on Tuesday, the latest in a series of maritime enforcement actions that is threatening to derail fragile peace negotiations between Washington and Tehran.

The Pentagon announced that US forces "conducted a right-of-visit maritime interdiction" and boarded the M/T Tifani "without incident" overnight. The vessel, capable of carrying around two million barrels of crude oil, was tracked near Sri Lanka and was reportedly close to fully loaded, with Singapore listed as its destination. US Central Command stated it would "pursue global maritime enforcement efforts to disrupt illicit networks and interdict sanctioned vessels providing material support to Iran — anywhere they operate," adding that "international waters are not a refuge for sanctioned vessels."

The boarding comes at a particularly sensitive moment. A two-week ceasefire — declared after the United States and Israel launched a military campaign against Iran on 28 February — is due to expire on the evening of 22 April. A first round of peace talks held in Islamabad, Pakistan's capital, produced no agreement ten days ago, and a second round remains uncertain. Iranian officials told Reuters that Tehran was "positively reviewing" attendance but had not made a firm decision, insisting that conditions including recognition of its right to enrich uranium must be met. US Vice President JD Vance was expected in Islamabad, and Pakistani officials indicated that if delegations did attend, they would not arrive until Wednesday — leaving precious little time to reach a deal before the truce expires.

Iran has consistently argued that the US blockade of its ports constitutes a violation of the ceasefire, and that the seizure of vessels makes negotiations impossible. Iran has also largely blocked the Strait of Hormuz — the narrow waterway connecting the Persian Gulf to the wider ocean, through which roughly 20 million barrels of oil typically pass each day — closing it to all but its own ships. Though Iran announced last week it would reopen the strait, it reversed that decision after Washington declined to lift its blockade. President Donald Trump, meanwhile, said the US was in a "very strong" negotiating position and warned that military strikes on Iran would resume if no deal was reached, telling CNBC: "The military is raring to go."

The conflict has already killed thousands of people and sent shockwaves through global energy markets, with fears of a broader economic recession growing. Oil prices have swung sharply in recent days on uncertainty about the talks, while Asian equity markets edged higher on Tuesday on cautious hopes that negotiations could still resume. The coming hours will be critical in determining whether diplomacy can prevent a return to open warfare.