Iran vowed Wednesday not to reopen the Strait of Hormuz so long as a US naval blockade remained in place despite a ceasefire extension, as it announced the seizure of two ships trying to cross the strategic waterway.

As the clock ticked for a return to the war that has engulfed the region, US President Donald Trump had said Tuesday he would maintain the truce to allow more time for Pakistani-brokered peace talks.

Iran said it welcomed the efforts by Pakistan but made no other comment on Trump's announcement.

"A complete ceasefire only has meaning if it is not violated through a naval blockade," said Iranian parliament speaker Mohammad Bagher Ghalibaf, who led Tehran's delegation in the first round of talks in Islamabad.