Washington (AFP) - After months of piling pressure on Tehran, the United States is seeing an unexpected new variable -- the novel coronavirus, which has taken a substantial toll not just on Iran but inside its government.

US policymakers are asking whether deaths within the regime are widespread enough that they could alter decision-making -- although a deadly rocket attack Wednesday in Iraq, which Washington blamed on Iran, showed at least that the cycle of conflict between the countries is not abating.

COVID-19, which has infected tens of thousands of people around the world, has hit Iran's government unusually hard, with a number of senior politicians and officials killed or infected by the disease including a vice president, a senior adviser to the foreign minister and a powerful cleric.

General Kenneth McKenzie, head of Central Command which covers the Middle East, said the United States believed the impact was worse than the more than 500 deaths reported -- the world's third highest toll after China and Italy -- and said US policymakers were assessing the political ramifications.

"Of course, death is permanent," McKenzie told reporters Friday.

"In the short term, it's going to make it a lot harder to make decisions. People are separated."

A day earlier, McKenzie told a Senate hearing that the health crisis -- two months after Iranian public outrage over the accidental downing of a civilian Ukrainian plane -- made the leadership "more dangerous" as it would likely seek to "unite the masses of its people against an external target."

"There is very little evidence in the history of warfare of a regime that has a crippling internal problem that decides to focus on the crippling internal problem," he said.

- Weakened by US sanctions -

President Donald Trump, closely allied with Iran's regional adversaries Saudi Arabia and Israel, has sought to debilitate the Shiite clerical regime through sweeping sanctions including on Iran's key export of oil.

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Nearly two years ago, Trump bolted from an agreement brokered by his predecessor Barack Obama under which Iran drastically scaled back nuclear activities in return for promises of economic relief.

Even with Trump exempting humanitarian goods from sanctions, few companies are willing to risk US wrath by selling to Iran.

"The current crisis in Iran is really one that has been the result of the government's own missteps in its policies rather than the American sanctions," said Amir Afkhami, a professor at George Washington University who has studied Iran's public health system.

"But the American sanctions have certainly contributed to worsening an already very bad situation."

Iran has historically boasted one of the region's strongest public health systems. Afkhami cited unconfirmed reports that some officials have flown to Lebanon for treatment as a sign of the burden on Iranian hospitals.

While Iran recently ordered a nationwide lockdown for coronavirus testing, Afkhami said action had come too late.

Reliant on Chinese trade in the face of US sanctions, Iran failed to cut off air links with China when the epidemic emerged and as late as February was still exporting domestically-made face masks, Afkhami said.

"As a physician, I can say it would make sense that the disease has taken a particularly significant toll amongst Iran's aging leadership.

"How much that has arrested the ability of the leadership to make policy decisions, that's very difficult for me to say, partly because the policy towards the coronavirus was anemic even before the outbreak made its way into Iran."

- Regime still standing -

Trump has volunteered to assist Iran, with the State Department communicating US willingness formally through Swiss intermediaries, although it was unclear if Washington has made concrete offers or if Tehran would accept them.

One key test will be if the United States blocks Iran's request for an IMF loan -- the first sought by Tehran since the late shah's era.

Barbara Slavin, director of the Future of Iran Initiative at the Atlantic Council, doubted the impact of coronavirus deaths on the sprawling leadership.

"Iran has experienced extraordinary pressure since the US imposed the oil embargo, with blow after blow, but the regime is still there," she said.

The big exception, she said, would be if the pandemic somehow reaches Supreme Leader Ayatollah Ali Khamenei, an 80-year-old whose health has long been the subject of speculation.

Khamenei has described COVID-19 as a biological weapon, a charge Washington scoffed at.

With Trump under fire at home over his handling of the outbreak, a rocket attack Wednesday on an Iraqi base killed two US personnel and a British soldier.

The United States attributed the attack to a pro-Iranian paramilitary force and launched retaliatory air strikes -- the latest round in a conflict that included the US killing of a top Iranian general, Qassem Soleimani, in January.

"I think this pattern will continue, especially because the Trump administration, like so many other governments, is completely distracted," Slavin said.

"The calculation in Iran must be that he can't handle one crisis, so how can he handle two at the same time?"