Two strategic US bombers have flown over the Persian Gulf in response to what US officials say are worrying signs that Iran may be planning attacks against American or allied targets in the Middle East in the coming days.

The B-52 bomber mission, flown round trip from Minot Air Force Base in North Dakota on Wednesday, December 30, was the second of its kind this month. The missions reflect growing concern in Washington, in the final weeks of President Donald Trump’s administration, that Iran will order further military retaliation for the US government's killing last January 3 of top Iranian military commander General Qasem Soleimani.

With the first anniversary of his death days away, the media and officials in Iran are portraying Soleimani as an Iranian hero and international Islamic figure. Top officials call for revenge against the United States on daily basis. The current commander of the Qods (Quds) Force, Esmail Ghaani and President Hassan Rouhani, among others, renewed these calls on Wednesday.

Adding to the tension was a rocket attack last week on the US Embassy compound in Baghdad by Iranian-supported Shiite militia groups. No one was killed, but Trump tweeted afterward that Iran was on notice.

"Some friendly health advice to Iran: If one American is killed, I will hold Iran responsible. Think it over,” Trump wrote on Dec. 23.

In announcing Wednesday's bomber flight, the head of US Central Command said it was a defensive move, while not mentioning Iran by name.

“The United States continues to deploy combat-ready capabilities into the US Central Command area of responsibility to deter any potential adversary and make clear that we are ready and able to respond to any aggression directed at Americans or our interests,” said Gen. Frank McKenzie, the commander of Central Command. “We do not seek conflict, but no one should underestimate our ability to defend our forces or to act decisively in response to any attack.”

While Iranian officials call for revenge for Soleimani’s killing, they need to be cautious during the remaining weeks of Trump’s presidency and also consider not spoiling a chance of improving ties with Joe Biden who might be more willing to ease tensions.

But an unnamed senior military officer told the Associated Press that Iran may be considering or planning “more complex” and broader attacks against American targets or interests in the Middle East. The officer mentioned advanced weapons flowing from Iran into Iraq recently and indications that Iraqi Shiite militia leaders may have met officers of the Qods Force.

He added that Iran may be considering attacks on economic targets similar to the destructive drone and missile attack in September 2019 on Saudi Arabia’s oil installations.

While the US military has taken steps to signal its willingness to act in case of an Iranian adventure, it has also indicated there are no plans or orders to take unprovoked action against Iran. The B-52 flights this month and the transit of a US guided-missile submarine last week through the Strait of Hormuz were meant as clear defensive signals.

With reporting by AP