Iran’s supreme leader defiantly vowed Thursday to protect the Islamic Republic’s nuclear and missile capabilities, which U.S. President Donald Trump has sought to curtail through airstrikes and as part of a wider deal to cement the war’s shaky ceasefire.

In a statement read by a state television anchor, Ayatollah Mojtaba Khamenei said the only place Americans belonged in the Persian Gulf is “at the bottom of its waters” and that a “new chapter” was being written in the region’s history. Khamenei has not been seen in public since taking over as supreme leader following the killing of his father in the war’s opening airstrikes.

His remarks come as Iran’s economy is reeling and its oil industry is being squeezed by a U.S. Navy blockade halting its tankers from getting out to sea. The world economy is also under pressure as Iran maintains its chokehold on the Strait of Hormuz, through which a fifth of all crude oil is transported. On Thursday, the global benchmark for oil, Brent crude, traded as high as $126 a barrel.

That shock to oil supplies and prices is putting pressure on Trump, who is floating a new plan to reopen the critical passageway used by the U.S.'s Gulf allies to export their oil and gas.

Under the plan, the U.S. would continue its blockade on Iranian ports, while coordinating with allies to impose higher costs on Iran’s attempts to subvert the free flow of energy, according to a senior administration official, who spoke on condition of anonymity because they were not authorized to comment publicly.

In a cable sent Tuesday, the U.S. State Department instructed American diplomats around the world — except those in Belarus, China, Cuba and Russia — to seek their host government’s support for the Trump administration’s call for assistance in establishing a “maritime freedom construct” that would ensure free and unimpeded access to shipping through the strait.