The U.S. Navy is escorting ships through the Strait of Hormuz despite the threat from Iran, guiding more than 20 crude oil carriers on some nights, Interior Secretary Doug Burgum said.

Some are ultra-large tankers that hold 2 million barrels of crude, Burgum said Friday on CNBC.

The comments add detail to the claims made by President Donald Trump in recent days that the United States has made progress in facilitating the trade of oil through the strait, a development that would give the U.S. significant leverage over the Iranian regime in peace negotiations. The effective closure of the shipping in recent months by Iran has crimped the global supply of oil, driving up prices for fuels and undermining public support for Trump.

“If you’re talking 20 ships out a night, you’re talking substantial amounts of oil that have come out of the strait,” Burgum said. 

Trump this week claimed that the U.S. has taken 100 million barrels of oil out of Iran, an offhand comment made in the Oval Office that generated some confusion among oil market observers. The president said he directed a secret military mission last month to support oil tankers and commercial ships in the strait, which resulted in more than 100 million barrels of oil to flow out of the strait and into the open market. 

Burgum noted that the president’s Project Freedom, a plan to escort ships out of the Strait of Hormuz, was halted in May. He said, though, that it was restarted “without any fanfare publicity with Navy ships.”

Since the war in Iran began in late February, shipping through the strait has been at a standstill, disrupting global trade of oil, gas, and other key economic commodities. Before the war, nearly 20 million barrels of crude oil and other products passed daily through the strait, equivalent to 20% of global oil demand. 

It is a risky route because it is a narrow waterway, making it difficult to maneuver through if Iranian forces threaten passage. Yet the U.S. strategy has been to escort ships through a route that hugs close to the coast of Oman, protected by the Navy and air cover, the Financial Times reported.

Trump this week threatened to continue strikes against Iran and to take over Kharg Island, which is a small island located about 16 miles off the Iranian coast that handles millions of barrels of oil a day. 

But, Trump reversed his plans yesterday to strike Iran overnight after approved discussions with Iranian leadership, and teased a ceasefire deal between Washington and Tehran. Oil prices dropped following the announcement but have remained relatively high, fluctuating between $90 and $100 per barrel.