Brent crude briefly crossed $90 a barrel and U.S. gasoline returned to $4 a gallon on Monday as American forces completed a ninth consecutive night of strikes against Iranian targets and the Pentagon disclosed the death of a third U.S. service member in the past week, pushing the U.S. war-dead toll to 17.

The moves marked the sharpest reassertion of a war premium in the energy market since a June 17 interim agreement briefly reopened the Strait of Hormuz. Brent for September delivery pared its gain to trade 0.4 percent higher at $88.47 a barrel after touching above $90 earlier in the session. U.S. West Texas Intermediate for August delivery slipped 0.2 percent to $82.36. The national average pump price hit $4 for the first time since the June accord was signed, according to AAA.

The strait, which normally handles about 20 percent of the world's seaborne oil trade, has seen shipments fall sharply in the latest cycle of attacks. Iran's Islamic Revolutionary Guard Corps renewed its pledge that "not a single drop of oil, gas, or chemical fertilizer" would move through the waterway while U.S. strikes continue.

What shifted

U.S. Central Command said its overnight wave hit military sites and communications networks across Iran to "further diminish" Tehran's attacks on shipping. Iran's semi-official Tasnim news agency reported strikes on Tabriz, Chabahar, Konarak, Bandar Mahshahr and Bandar Imam Khomeini. Iranian state media reported that two oil tankers exploded in the strait; the Revolutionary Guard said the vessels had used what it called an "unsafe and hazardous southern route" and had been "brought to a halt." Centcom disputed the claim.

Iran said its own overnight response included a "surprise attack" in Syria and strikes on U.S. aircraft at Jordan's Aqaba airport. Kuwait's armed forces said they had intercepted Iranian drones.

On the Street

Amrita Sen, founder and director of research at Energy Aspects, told CNBC that depleted inventories and slower Hormuz traffic could push crude past $100 a barrel. Sen said, "Do we think prices should or could go to triple digits? Absolutely." She added, "Remember the market is short as well, right? It was a market that went heavily short as soon as Hormuz was starting to reopen, that's why we went into the seventies."

Sen said macro fund clients were still discounting the shock. She told CNBC, "The market is still quite complacent despite the price increase we have seen."

The casualties

The Pentagon on Sunday confirmed a third U.S. service member had been killed in the current cycle, dying in northern Iraq during what Centcom called "a controlled detonation of unexploded ordnance" from a downed Iranian attack drone. A second soldier was wounded. Investigators searching the site of Friday's Iranian strike on Muwaffaq Salti Air Base in Jordan recovered "unidentified remains," and a Navy pilot missing earlier this month was declared dead, taking the U.S. death toll in the war to 17.

The Pentagon identified the two soldiers killed in Jordan as Isabella Gonzales, 19, and Tyler James Feehan, 25. President Trump said the new wave of strikes had hit Iran "very hard" and had been carried out "in honour" of the three service members killed in Jordan and Iraq.

Secretary of State Marco Rubio said Washington "always remains open to a diplomatic solution" but insisted "the world has to decide whether or not it's going to allow an international waterway to be under the control" of Iran. Iran's Foreign Ministry spokesman Esmail Baghaei told reporters intermediaries had continued to exchange messages during the strikes and that talks with the U.S. could be pursued based on national interests.

The counterpoint

The case against another pause came Sunday from Steve Forbes, chairman and editor-in-chief of Forbes and a former presidential candidate, who told Fox News Digital at Freedom Fest in Las Vegas that the administration should refuse a second ceasefire. Forbes said, "Going back to Thomas Jefferson, a core foreign policy plank of the United States is freedom of the seas." He invoked the War of 1812 and U.S. campaigns against the Barbary pirates and added, "The Strait of Hormuz is an international waterway, just as the South China Sea is an international waterway. And so we must keep that open." Forbes said proper use of air power should preclude ground troops but urged Trump to press on. "Get Iran done with. No more fake ceasefires."

The June 17 preliminary agreement collapsed within weeks. Trump declared it "over" on July 8, and negotiators have made little visible progress since. Gasoline last touched $4 a gallon the day the accord was signed.