WASHINGTON, March 1 (Reuters) - U.S. President Donald Trump warned on Sunday that combat operations in Iran were continuing and would carry on until all of Washington's objectives are achieved.

Trump confirmed in a video posted on Truth Social that three U.S. service members had been killed and said there would likely be more casualties, vowing to avenge the deaths of Americans.

"Combat operations continue at this time in full force, and they will continue until all of our objectives are achieved. We have very strong objectives," Trump said.

March 1 (Reuters) - U.S. President Donald Trump suggested the conflict with Iran could go on for the next four weeks, the Daily Mail newspaper reported on Sunday.

"It's always been a four-week process. We figured it will be four weeks or so. It's always been about a four-week process so - as strong as it is, it's a big country, it'll take four weeks - or less," the British newspaper quoted Trump as saying.

Trump told the newspaper he remained open to more talks with the Iranians, but did not say if that would happen "soon."

Dubai has been transformed into a major global economic hub through diversification in sectors such as transportation, finance and tourism, to reduce its dependency on fossil fuels.

The emirate, along with several Middle Eastern cities such as Doha and Manama, was hit on Sunday morning by a series of explosions, the day after attacks by Iran in the Gulf in response to US-Israeli strikes that killed the Islamic republic's supreme leader Ayatollah Ali Khamenei.

March 1 (Reuters) - Ukrainian President Volodymyr Zelenskiy said on Sunday that the changes in Iran brought about by U.S. and Israeli strikes should be "used properly" to benefit the country's people who had withstood violence from their authorities.

Zelenskiy, speaking in his nightly video address, said Iran's authorities had killed "tens of thousands of people in the last couple of months alone," referring to a crackdown on protests.

On a US late-night television show Saturday, the host played a clip from 2011 of a businessman warning that president Barack Obama "will start a war with Iran because he has absolutely no ability to negotiate."

That businessman was Donald Trump. Fast-forward 15 years and Trump, now in his own second term as president, ordered huge military strikes on Iran when talks with Tehran brought no breakthrough.

By Lili Bayer and Andrew Gray

BRUSSELS, March 1 (Reuters) - The European Union's 27 nations on Sunday called for "maximum restraint" and full respect for international law in the Iran conflict, EU foreign policy chief Kaja Kallas said.

"We call for maximum restraint, protection of civilians and full respect of international law, including the principles of the United Nations Charter, and international humanitarian law," said a statement issued by Kallas on behalf of all EU members.

France, Germany and the UK said Sunday they were ready to defend their interests and those of its allies in the Gulf if necessary by taking "defensive action" against Iran.

The three countries' leaders were "appalled by the indiscriminate and disproportionate missile attacks launched by Iran against countries in the region, including those who were not involved in initial US and Israeli military operations", said the joint statement.

By Samia Nakhoul, Parisa Hafezi and Emily Rose

DUBAI, March 1 (Reuters) - The assassination of Iran's Supreme Leader Ayatollah Ali Khamenei has plunged the Islamic Republic into its most perilous crisis since the 1979 revolution - confronting it with war on its own territory, an unresolved succession, and mounting internal strain.

DUBAI, March 1 (Reuters) - Israeli strikes hit a hospital in Tehran’s Gandhi Street area, two witnesses told Reuters on Sunday, saying the hospital was badly damaged and patients were being taken out.

(Reporting by Parisa HafeziEditing by Peter Graff)

By Doina Chiacu

March 1 (Reuters) - The United States has yet to spell out a "day-after" strategy for Iran following joint U.S.-Israeli strikes that killed much of the country's leadership, lawmakers from both major political parties said on Sunday.