Iran's military warned on Wednesday it would block trade through the Red Sea, along with the Gulf and Sea of Oman, if the US naval blockade on Iranian ports continues.
In a statement carried by Iranian state television, the head of the military's central command centre said if the US continues with its blockade and "creates insecurity for Iran's commercial vessels and oil tankers", it will also constitute "a prelude" to violating the ceasefire.
"The powerful armed forces of the Islamic republic will not allow any exports or imports to continue in the Persian Gulf, the Sea of Oman, and the Red Sea," said Ali Abdollahi.
He added that Iran will "act decisively to defend its national sovereignty and its interests".
The United States has imposed a naval blockade on Iranian ports since Monday after US-Iran talks over the weekend in Pakistan failed to produce a deal to end the war.
But maritime tracking data on Tuesday indicated that several ships sailing from Iranian ports had crossed the Strait of Hormuz despite the blockade.
On Wednesday, Iran's Tasnim news agency quoted unnamed informed sources as saying that shipping from Iran's southern ports had continued.
It added that Iranian "commercial vessels have set sail for various destinations around the world" during the past 24 hours.