Donald Trump says he had trouble keeping the "secret mission" a secret. (Reuters: Evan Vucci)
In short:
US President Donald Trump says a "secret" military mission has been supporting commercial shipping in the Strait of Hormuz, getting around Iran's blockade and keeping oil prices down.
Maritime tracking firms have observed some journeys through the strait during the blockade, but ships' transponders have reportedly been turned off, making tracking efforts difficult.
The reported resumption in shipping is well below levels recorded before the war, when more than 100 commercial vessels traversed the strait daily.
Donald Trump says the US has secretly helped ships move significant amounts of oil through the Strait of Hormuz, defying an Iranian blockade.
The US president said his military had been running a "secret mission" to support tankers and commercial ships through the strait.
"This wildly successful effort is because the UNITED STATES of AMERICA CONTROLS the Strait of Hormuz — NOT Iran," Mr Trump wrote on social media.
The president initially made the claim during an Oval Office press conference. He revealed few specifics and produced no evidence, but told reporters he could announce the news because Iran had now "figured it out".
In his later social media post, he said more than 200 commercial ships had travelled through the strait, carrying more than 100 million barrels of oil.
The ABC and US outlets have previously reported on "dark" journeys taken by ships through the strait, though some are understood to have involved coordination with Iran rather than the US Navy.
Many vessels had reportedly turned off their transponders to avoid detection, making shipping movements difficult to track and verify.
Other monitors had recorded different figures using different methods. Trade tracking company Kpler said it had recorded 264 ships exiting the Persian Gulf between the start of the ceasefire and early June.
On May 31, The New York Times, citing unnamed officials, reported the US military had guided about 70 commercial ships through the strait in recent weeks.
Banking giant JPMorgan estimates that more than a million barrels of oil a day may have been passing through the strait, CNN reported earlier this week.
In a recent note to clients, JPMorgan said: "Despite the ongoing naval blockade and the steep decline in commercial traffic, surprising volumes of crude and petroleum products still appear to be transiting the Strait."
Before Iran's blockade and attacks on ships, more than 100 commercial vessels crossed the strait each day, so the reported resumption in movements is well below pre-war levels.
But Mr Trump said the mission had held off higher hikes in oil prices. He said he had found it difficult to keep the operation confidential.
"I wanted to say it so badly," he told reporters in the Oval Office. "I didn't want to ruin it, but it was very hard."