The United States has denied Iranian claims that the Strait of Hormuz has been closed, saying commercial shipping continues to move through the key global oil route.
Iran had earlier said it was shutting the strategic waterway and accused the US and Israel of violating a ceasefire agreement amid rising tensions linked to Israeli strikes in Lebanon.
The conflicting accounts come as uncertainty grows over regional stability and the future of a fragile US-Iran agreement.
Iran's Revolutionary Guard Corps Navy said it had closed the Strait of Hormuz to all vessels, citing what it described as ceasefire violations by the United States and Israel.
The military also issued a warning to ships, saying: "Do not approach the Strait of Hormuz; otherwise, your security will be jeopardized."
However, US officials strongly disputed those claims, insisting maritime traffic through one of the world's most important shipping lanes remained unaffected.
A spokesperson for US Central Command (Centcom) said that "traffic continues to flow" through the strait and that American forces were "monitoring the situation".
In a statement posted after Iran's announcement, Centcom said commercial activity had increased rather than declined.
"Commercial ship traffic in the Strait of Hormuz increased June 20 as US forces continued operating in the general area to support freedom of navigation," the statement said.
It added that "safe passage through the international waterway remained intact today as 55 merchant ships transited, moving large amounts of cargo and more than 17 million barrels of oil to global markets".
US Vice-President JD Vance also rejected reports suggesting Iran had effectively shut the route.
"We're not seeing any evidence that the Iranians are still closing down the Strait of Hormuz," he told Fox News.
"We actually got 16 million barrels of oil out of the Strait of Hormuz yesterday. So you're seeing those ships move," he added.
The disagreement comes amid wider tensions in the region, with Israel and Hezbollah accusing each other of violating a new ceasefire arrangement. The dispute has raised fresh questions over the future of a broader agreement between Washington and Tehran.
Pakistan's foreign ministry said talks involving US and Iranian representatives are expected to take place in Bürgenstock, Switzerland, with Pakistan and Qatar acting as mediators.
According to the ministry, the discussions are intended to advance understandings reached under a 14-point memorandum of understanding.
The Strait of Hormuz remains strategically important because a significant share of the world's oil trade passes through the waterway, making any threat of disruption closely watched by global markets and governments.