Fighting intensified this week and continued on Saturday after the US said it had carried out strikes on more than 140 targets across Iran.
Washington said the attacks were launched in response to Iranian forces striking a commercial vessel transiting the Strait of Hormuz, alleging the ship was travelling along an unauthorised route.
Iran, which has sought to tighten control over the vital shipping lane, announced early Sunday that the strait would remain closed until further notice.
The Islamic Revolutionary Guard Corps (IRGC) also launched large-scale attacks on US military bases and allied countries across the region on Sunday, marking a significant escalation in the conflict.
Iran said it had targeted a US military base in Jordan, while the United Arab Emirates, Qatar, Kuwait, Oman and Bahrain reported intercepting Iranian missiles and drones.
Qatar, which has been mediating ceasefire negotiations, had not faced an attack since April, while the UAE had not been targeted since May.
The renewed violence has placed last month s interim ceasefire agreement under severe strain. The agreement aimed to reopen the Strait of Hormuz and lay the groundwork for a permanent end to the conflict.
Earlier this week, US President Donald Trump declared that Iran s latest attacks had effectively ended the ceasefire, while Iranian Foreign Minister Abbas Araghchi accused Washington of violating the agreement.
Despite the breakdown, Trump said negotiations would continue, with mediators working to revive the diplomatic process.
According to US media reports, Iran informed American officials that earlier attacks on commercial tankers had been accidental and blamed a rogue internal group.
The latest escalation began after the IRGC said it had fired a naval cruise missile at a vessel sailing along what it described as an unauthorised route.
US Central Command (CENTCOM) said the IRGC had "blatantly attacked" the Cyprus-flagged MV GFS Galaxy, leaving the vessel unable to continue its voyage after sustaining damage to its engine room.
CENTCOM also confirmed that one crew member was missing.
The United Kingdom Maritime Trade Operations (UKMTO) said military authorities had informed it that the vessel s crew abandoned ship and escaped in a lifeboat.
"Iran was provided yet another opportunity to demonstrate adherence to the Memorandum of Understanding after being held accountable for earlier attacks on commercial vessels but has again failed," CENTCOM said in a statement posted on X.
The US military said its strikes targeted 140 Iranian military sites, including missile and drone facilities, communications infrastructure and coastal surveillance positions.
US Defence Secretary Pete Hegseth shared the statement, writing: "Iran made a poor choice. Now they pay."
The IRGC confirmed that US strikes had hit several coastal military bases and telecommunications facilities in southern Iran.
In retaliation, Iran said the first phase of its response included missile strikes on Jordan s Prince Hassan Air Base, claiming it had destroyed the base s command centre and MQ-9 drone hangars.
On Sunday, CENTCOM reiterated that the Strait of Hormuz remained open and said US forces were positioned to ensure freedom of navigation through the waterway.
Earlier, Iran s parliamentary speaker and chief negotiator with the US, Mohammad Bagher Ghalibaf, wrote on X that the "era of one-sided deals is over."
"We told you: keep your word or pay the price. Reality is knocking," he added.
