Seventeen U.S. service members have been killed since the war in Iran began.
President Donald Trump announced "major combat operations" against Iran on Feb. 28, with massive joint U.S.-Israeli strikes targeting military, government and infrastructure sites.
Delegations from the U.S. and Iran entered negotiations in June aimed at a war-ending deal based on a memorandum of understanding signed by both countries.
The U.S. and Iran have nonetheless continued to exchange strikes, with the strategic Strait of Hormuz the primary flashpoint.
The Islamic Revolutionary Guard Corps claimed on Tuesday morning that the Strait of Hormuz remains closed to commercial traffic.
"Not a single drop of oil or gas, nor any shipment of chemical fertilizers, will be exported from the region as long as the United States continues its hostile actions," the force said in a statement.
-ABC News' Nasser Atta and Joe Simonetti
Bahrain's Interior Ministry said on Tuesday morning that air raid sirens were sounded, urging residents "to remain calm and head to the nearest safe place."
The State Department issued a "worldwide caution" for American citizens early on Tuesday "due to heightened tensions in the Middle East."
"The security environment remains complex with the potential for unforeseen escalation," read the statement, which was shared by regional embassies. "Americans currently in the Middle East should exercise caution and heightened vigilance and should be prepared for possible flight cancellations, periodic airspace closures and potential travel disruptions."
"Please monitor embassy and consular security alerts, local authorities, and the news for breaking developments. Americans outside the Middle East should reconsider travel to and through the region," it added.
"U.S. diplomatic facilities, including outside the Middle East, have been targeted. Iran and groups supportive of Iran may target other U.S. interests overseas or at locations associated with the United States and Americans throughout the world," the statement said.
U.S. Central Command said late on Monday that it completed its 10th consecutive night of strikes on Iran.
The attacks targeted "Iranian military command centers, maritime capabilities, missile and drone launch sites, and air defense systems to degrade Iran's ability to continue attacking commercial vessels flowing through the Strait of Hormuz," CENTCOM said in a post to X.
-ABC News' Alex Ederson
