The attacks cast more doubt on a tenuous month-old ceasefire that the United States has insisted is still in effect.

President Trump said late Thursday that the temporary truce with Tehran remains intact despite U.S. forces hitting military targets in Iran. The latest strikes came after Tehran attacked American-guided missile destroyers that were transiting the Strait of Hormuz,

Washington and Tehran are trading blows as their negotiators seek a deal to end the fighting, but so far they’ve avoided a return to all-out fighting.

The renewed hostilities broke out as Washington was awaiting Iran's response to a U.S. proposal that would stop the fighting but leave the most contentious issues, such as Iran's nuclear program, unresolved for now.

The "self-defense strikes" followed attacks on three American naval vessels, U.S. Central Command said in a statement. None of the U.S. warships were hit.

The White House reportedly believes it could be closing in on a 14-point memorandum of understanding with Iran.

World shares have mostly retreated and oil prices fell again after climbing as the fragile ceasefire with Iran was strained by missile and drone attacks that prompted U.S. retaliatory strikes on Iranian military facilities.