The United States said Thursday that Iranian authorities may have killed more than 1,000 people in a crackdown on demonstrations, which Washington cast as the clerical regime's worst-ever internal challenge.
The damning account came as the US put new pressure in the region on its arch-enemy, with an official saying the Pentagon was considering sending 5,000 to 7,000 more troops.
"It appears the regime could have murdered over 1,000 Iranian citizens since the protests began," Brian Hook, the US pointman on Iran, told reporters.
He acknowledged that information was difficult to verify in Iran, which has severely curtailed the internet, but said: "We know for certain it is many, many hundreds."
Hook said that "many thousands" of Iranians have been wounded and that at least 7,000 protesters have been detained.
President Donald Trump, receiving UN diplomats at the White House, called the crackdown "brutal" and a "horrible situation" as he vowed to respond "strongly" to any threat from Iran against US interests.
Protests broke out on November 15 across Iran, whose economy has suffered under sweeping sanctions from the United States, after the government abruptly hiked fuel prices.
Hook said the ensuing crackdown showed that the regime has had to rely on brute force and was losing support even with its traditional working-class base.
"This is the worst political crisis the regime has faced and its 40 years," Hook said.
- Figure of opposition group -
The death toll is sharply higher than the figure of 208 dead given by Amnesty International, which said it was cautious due to difficulties in verifying information.
But the toll matches the figure of 1,029 dead released Wednesday by the Mujahedin-e-Khalq, the formerly armed opposition that is fiercely critical of the regime and has cultivated close ties with the Trump administration.
Hook said the US was basing its toll in part on photos and videos sent by 32,000 people after Secretary of State Mike Pompeo invited Iranians to defy internet restrictions.
Hook said videos sent from Mahshahr, a southwestern city home to many from Iran's Arab minority, showed the elite Revolutionary Guards chasing protesters into marshlands with machine-guns mounted on trucks.
"They then spray the protesters with bullets. Between the rounds of machine-gun fire, the screams of the victims can be heard," Hook said, charging that as many as 100 people were killed there alone.
Iran has dismissed the high death tolls as "utter lies" and confirmed only five dead -- four security force personnel killed by "rioters" and one civilian.
But in a softening of stance that indicates a need to address grievances, Iran's leader, Ayatollah Ali Khamenei, said that people killed in the violence would be considered "martyrs" as long as they did not foment the unrest.
- US considers more troops -
As Hook demanded further diplomatic isolation of Iran, a senior Pentagon official did not rule out sending more forces to the region.
"We're continuing to look at that threat picture and have the ability to dynamically adjust our force posture," John Rood, the Pentagon's policy chief, told a Senate hearing.
A US official told AFP on condition of anonymity that Defense Secretary Mark Esper was considering plans to move between 5,000 and 7,000 troops to the Middle East.
The official did not confirm where the troops would be sent or in what timeframe.
But both Rood and Esper denied a report in The Wall Street Journal that the United States was considering sending 14,000 more troops -- equivalent to the number sent over the past six months.
Tensions have risen sharply with Iran since Trump last year pulled out of a denuclearization pact and sought to ban all of Iran's oil exports.
In September, the United States said Iran was responsible for attacks on the major Abqaiq oil processing center in Saudi Arabia.
The United States has also been alarmed by an uptick in attacks on its bases in Iraq, where major demonstrations triggered by economic discontent have also targeted Tehran's overwhelming influence in its Shiite-majority neighbor.
"We're lucky no one has been killed. There is a spike in rocket attacks," another US official said, adding that the sophistication showed the attacks were not from the Islamic State group.
Hook said that a US warship on November 25 seized a major shipment of Iranian-made weapons bound for Yemen's Huthi rebels, who are battling a Saudi onslaught, including anti-tank and air-defense missiles.
Britain, France and Germany, which still back the nuclear deal, in a joint letter to the United Nations also accused Iran of developing nuclear-capable ballistic missiles.
Iranian Foreign Minister Mohammad Javad Zarif called the allegation a "desperate falsehood" and accused the Europeans of "bowing to US bullying."