TEHRAN/WASHINGTON/MUSCAT/JERUSALEM - Iran on Monday warned of "much more devastating" and extensive retaliation if its civilian targets are further attacked.

"If attacks on civilian targets are repeated, the next stages of our offensive and retaliatory operations will be much more devastating and widespread," said a spokesman for the Khatam al-Anbiya Central Headquarters.

Earlier, US President Donald Trump threatened to destroy Iran's civilian infrastructure if the Strait of Hormuz remains closed.

In another development, Ali Akbar Velayati, adviser to Iran's supreme leader, warned on Sunday that the resistance front could target the Bab el-Mandeb Strait.

"If the White House thinks of repeating its stupid mistakes, it will quickly realize that the flow of global energy and trade can be disrupted with a single signal," Velayati said on social media, hinting at the possible closure of the waterway.

Connecting the Red Sea to the Gulf of Aden, the Bab el-Mandeb Strait is a key chokepoint for shipping between the Atlantic, Indian Ocean and Mediterranean.

Trump post

Trump posted "Tuesday, 8:00 p.m. Eastern Time!" on social media on Sunday, a message that appeared to signal a possible extension of the deadline for Iran to reopen the Strait of Hormuz.

On March 21, Trump threatened to "hit and obliterate" Iranian power plants if the country fails to fully open the strait within 48 hours. Two days later, he postponed strikes on power plants for five days, claiming to have held "productive conversations" with Tehran.

On March 26, Trump again pushed the deadline back, saying that he will pause planned strikes on Iranian energy facilities for 10 days, to April 6, the upcoming Monday at 8 pm Eastern Time. On Saturday, Trump reaffirmed that Iran has 48 hours to strike a deal on opening up the strait or face "Hell."

However, in the post on Sunday, Trump appeared to hint at extending the deadline for Iran to reopen the strait for another time.

In a post earlier Sunday, the US president threatened that Tuesday would be "Power Plant Day, and Bridge Day, all wrapped up in one" for Iran, and again urged Iran to open the Strait of Hormuz.

In an interview with The Wall Street Journal on Sunday, Trump threatened to destroy all of Iran's power plants if the country's leaders don't agree to reopen the strait by Tuesday evening.

"If they don't come through, if they want to keep it closed, they're going to lose every power plant and every other plant they have in the whole country," Trump said.

In a phone interview with Fox, Trump said that a deal to end the conflict in Iran could be reached by Monday.

ALSO READ: Trump warns of 'hell' in Iran amid intensified strikes

However, Trump's optimism does not seem to be echoed by the other side. Iran has rejected a US proposal for a 48-hour ceasefire, which was recently sent through one of its "friendly countries," the semi-official Fars news agency reported Friday, citing a source.

Also on Sunday, Trump told Israeli media Channel 12 that the United States is engaged in "deep" negotiations with Iran to secure a ceasefire, while stressing that Washington will not "leave in the middle" of the conflict.

Trump said his administration is maintaining contacts with Iran through multiple channels, led by his advisors Steve Witkoff and Jared Kushner.

According to sources briefed on the talks, communication is being conducted through two tracks: indirect contacts mediated by Pakistan, Egypt and Türkiye, and direct exchanges between US envoys and Iranian Foreign Minister Seyed Abbas Araghchi.

ALSO READ: Iran says US C-130 military transport plane, 2 helicopters destroyed

The mediating countries are seeking to help both sides agree on measures that could allow an extension of the US-imposed deadline, the sources said, adding that recent phone calls between the parties have not yielded significant progress.

Trump told Channel 12 that there is "a good chance" that a deal could be reached before Tuesday's "deadline", but warned that failure to do so would prompt the United States to take "strong" action in the region.

Oman, Iran discuss Hormuz Strait security

Meanwhile, Oman and Iran held a meeting to discuss possible options to ensure the smooth flow of navigation through the Strait of Hormuz amid current regional tensions, Oman's Foreign Ministry said on Sunday.

Oman's Foreign Ministry said in a post on X that the two countries held a meeting on Saturday at the level of deputy ministers in the foreign ministries of the two countries, attended by specialists from both sides. 

During the meeting, experts from both sides presented a range of views and proposals, which will be further studied, said the ministry.

Israel's Haifa struck

Four people were missing and four others injured after a missile from Iran struck a residential building in Haifa, a city in northern Israel, police said on Sunday.

The wounded included an 82-year-old man and three others with minor injuries, among them a 10-month-old baby injured by shrapnel, according to local rescue services.

The attack caused heavy damage to the building, with one of its facades collapsing, according to photos from the scene.

The missile was part of several barrages fired toward northern and southern Israel in the evening, triggering air raid sirens across the regions.

Police said four people remained unaccounted for and that search operations were underway.

The attack came as the Middle East was engulfed in violence following a joint US-Israeli strike on Iran on Feb 28.

IRGC intel chief killed

Iran's Islamic Revolutionary Guard Corps (IRGC) said Monday that its intelligence chief Majid Khademi was killed in US-Israeli strikes.

Khademi was "martyred in the criminal terrorist attack by the American-Zionist enemy... at dawn today," the IRGC said in a statement quoted by local media. 

Overnight US and Israeli strikes on Tehran province also killed at least six children, said Tehran's emergency operations center.

According to the center, the victims, four girls and two boys, were all under the age of 10.

Japan prepares for summit with Iran

The Japanese government is arranging summit talks with Iran, Prime Minister Sanae Takaichi said Monday, local media reported.

"We are preparing dialogues at the leadership level at an appropriate time," Takaichi told a parliamentary committee in response to a question from an opposition lawmaker about Japan's diplomatic efforts amid the ongoing US-Israel-Iran conflict, according to Kyodo News.