Washington/IBNS: The United States has warned that Iran could attack Israel soon in retaliation after a senior officer was killed in Iran's embassy in Damascus, media reports said.

US President Joe Biden has warned that the attack could be as soon as on Sunday.

"I don't want to get into secure information but my expectation is sooner than later," Biden told reporters.

When he was asked about the message he wanted to send to Iran, the President said, "Don't."

Biden has cleared his country will support Israel if the attack comes as he has anticipated.

"We are devoted to the defence of Israel. We will support Israel. We will help defend Israel and Iran will not succeed," he said.

Iran has been on an alert since April 12 in anticipation of a retaliation.

On April 1, the attack on Iran's embassy in Damascus killed Iranian Revolutionary Guard Corps' overseas Quds Force and others. However, Israel has not claimed responsibility.

Iran's supreme leader Ayatollah Ali Khamenei said Israel "must be and will be punished".

In an address to a massive crowd on Eid, Khamenei said as quoted by Al Jazeera, "When they attack our consulate, it is as if they have attacked our soil."

"The malicious regime made a mistake on this matter, and it must be punished and will be punished," he added.

In his address, Khamenei also lashed out at the US and the UK for rallying behind Israel and support for the war.

"Western governments, in the past year’s events, openly displayed the wicked nature of Western civilization to the world," Khamenei said as quoted by Al Jazeera.

"The bloody events in Gaza have left a bitter taste for Muslims around the world during this year’s blessed Ramadan," he said.

Khamenei's comment comes in the backdrop of the Israeli military's attack on Gaza strip leading to the killing of more than 33,000 Palestinians.

Travel advisories

The Indian government on Friday advised citizens to avoid travelling to Iran and Israel until further notice given the "prevailing situation in the region".

In the wake of the threat, the US and Russia have issued similar travel advisories for their staff and citizens in the region.

The foreign ministry advised its citizens in the two countries to observe "utmost precautions about their safety and restrict their movements to the minimum".

It is feared that retaliation by Iran can widen the six-month-old conflict between Iran-backed Hamas militants and Israel in Gaza.