The White House says “all options remain on the table” for the United States to take military action against Iran, reiterating that Tehran would face “grave consequences” if the killings of antigovernment protesters continue.

During a news conference on Thursday, White House Press Secretary Karoline Leavitt said US President Donald Trump and his team had communicated to Iran that “if the killing continues, there will be grave consequences”.

“The president understands today that 800 executions that were scheduled and supposed to take place yesterday were halted,” Leavitt told reporters, without providing any evidence to back up the claim that the executions were stopped.

“The president and his team are closely monitoring this situation, and all options remain on the table for the president,” she added.

Her comments come just hours after Trump appeared to soften his tone after several days of threats against Iran, with the US president saying his administration would take military action against Tehran if more killings were carried out.

Thousands of Iranians have taken to the streets since late December last year in mass demonstrations that were sparked by soaring inflation and the steep devaluation of the local currency.

The protests have spread to cities and towns across Iran, and activist groups say more than 1,000 demonstrators have been killed in the unrest.

The Iranian government, which describes the protesters as armed rioters backed by the US and its major regional ally, Israel, has said more than 100 security officers have been killed in attacks during the demonstrations.

Al Jazeera is not able to independently verify these figures.

Softened rhetoric

After days of heightened tensions and fears of a US military attack on Iran, Trump on Wednesday dialled down the rhetoric, saying he had received assurances that the killings of demonstrators had stopped.

Iranian Foreign Minister Abbas Araghchi also denied that Tehran planned to execute any protesters. “Hanging is ‌out of the ‌question,” he ⁠told the Fox News broadcaster.

The foreign minister had earlier this week said Iran is ready for war if the US wants to “test” it.

“If Washington wants to test the military option it has tested before, we are ready for it,” Araghchi said in an interview with our colleagues at Al Jazeera Arabic on Monday.

‘Great deal of uncertainty’

It remained difficult on Thursday to get information about what was happening on the ground in Iran as a nationwide internet blackout hit the one-week mark, according to online monitor NetBlocks.

But a resident of the Iranian capital, Tehran, said that security had been heavily reinforced amid continued uncertainty.

“There is a big military presence on the streets of the capital and elsewhere,” said the resident, who spoke on condition of anonymity.

“There is a great deal of uncertainty. A lot of people are worried,” they said. “There is a lot of death, sadness and anger.”

A commander in Iran’s elite Islamic Revolutionary Guard Corps (IRGC) also said the country’s armed forces remained on high alert.

IRGC Ground Force Commander Brigadier General Mohammad Karami said the military was “ready at the highest possible level”, Iran’s state-run Press TV reported.

Separately, Iranian Defence Minister Aziz Nasirzadeh warned that the government would use all its capabilities to “suppress the savage armed terrorists” it claims are behind the unrest.

In comments broadcast on Iranian state television, Nasirzadeh reiterated previous claims by the government that the demonstrations were orchestrated by the US and Israel.

The “designers and executors of the riots should know that we are monitoring them”, he added.

Meanwhile, despite Trump’s softening tone, Washington issued fresh sanctions against Iran on Thursday morning over the protest crackdown.

The measures targeted Ali Larijani, the secretary of Iran’s Supreme National Security Council (SNSC), and several other officials, whom Washington accused of being the “architects” of the Iranian government’s “brutal” response to the demonstrations.