President Donald Trump on Wednesday backed away from days of angry rhetoric against Iran as the two countries tried to defuse a crisis over the American killing of Iranian military commander Qassem Soleimani.

In an address from the White House, Trump said the US did not necessarily have to respond militarily to Iranian missile attacks on military bases housing American troops in Iraq overnight. He said no Americans were harmed in the strikes.

“The fact that we have this great military and equipment, however, does not mean we have to use it. We do not want to use it. American strength, both military and economic, is the best deterrent,” he said.

“Our great American forces are prepared for anything. Iran appears to be standing down, which is a good thing for all parties concerned and a very good thing for the world,” he said.

Iranian foreign minister Mohammad Javad Zarif had said the missile strikes “concluded” Tehran’s response to the killing of Soleimani, who had been responsible for building up Iran’s network of proxy armies across the Middle East.

Trump’s reaction in the immediate aftermath of Wednesday’s missile attacks had been to say on Twitter that “All is well!” and that Washington was assessing damage.

That tweet and the comment by Iran’s foreign minister had acted to soothe some initial concerns about a wider war and calmed jittery financial markets. Oil prices slipped back after an early spike.

Trump stopped short of making any direct threat of military action against Iran but said the US “will immediately impose additional punishing economic sanctions on the Iranian regime” in response to what he called “Iranian aggression”. He offered no specific measures.

The semi-official Fars news agency described the US President’s remarks as a “big retreat from threats”.

Iranian forces fired missiles at military bases housing US troops in Iraq on Wednesday in retaliation for the killing in Iraq of Soleimani, raising the stakes in its conflict with Washington amid concern about a wider war in the Middle East.

Iranian supreme leader Ayatollah Ali Khamenei, addressing a gathering of Iranians chanting “Death to America”, said the missile attacks were a “slap on the face” of the US and said American troops should leave the region.

The Pentagon said al-Asad air base and another facility in Erbil in Iraq were struck.

An official said the Pentagon “had no confirmation” that any Americans had been killed.

Australia, Britain, Denmark, Poland and Sweden, whose troops are stationed in Iraq alongside American forces, also said that none of their service members had been killed.

In December 2018, Trump had visited American military forces at the Asad base. It was his first visit to troops stationed in a combat zone. The base is an Iraqi installation that has long been a hub for American military operations in western Iraq.

The base in Erbil has been a special operations hub, home to hundreds of troops, logistics personnel and intelligence specialists.