A State Department official said Thursday that 1,000 or more protesters may have been killed during weeks of unrest in Iran and that the United States has received video that shows troops firing machine guns mounted on trucks at protesters in one incident.

Brian Hook, the special representative for Iran, said the Trump administration will ask Congress to impose harsh sanctions on officials responsible for the alleged atrocities and mistreatment of thousands of protesters who have been imprisoned since anti-government demonstrations have convulsed Iran.

Administration officials, meanwhile, said they are considering an increase in the U.S. military’s footprint in the Middle East to counter what they say is an intensified threat from Iran and its armed proxy groups.

Hook gave a harrowing description of the government crackdown, including the torture and rape of captured protesters.

“As the truth is trickling out of Iran, it appears the regime could have murdered over 1,000 Iranian citizens since the protests began,” including at least a dozen children, Hook said at a State Department briefing. The United States believes that many thousands more have been wounded and that at least 7,000 people have been arrested, he said.

The State Department’s casualty numbers are much larger than estimates provided so far by independent groups. Amnesty International, for example, has confirmed about 200 deaths, though it said the number was likely to be much higher.

The numbers are impossible to confirm, said Hadi Ghaemi, director of the Center for Human Rights in Iran, based in New York.

“What is certain is that a major massacre happened in Iran by government forces and they are doing everything to hide it and not let the truth be known,” he said. “What we need more than anything else right now is a broad international community demand for details and the extent of this massacre to be investigated.”

Alireza Miryousefi, a spokesman for the Iranian mission to the United Nations, said casualty figures “at this point are purely speculative and highly inaccurate.” He said the results of an investigation will be made public when it is completed.

“The government will also try to compensate for damages that occurred [through] vandalism or foreign-motivated and instigated riots imposed on ordinary citizens,” he added.

Behnam Ben Taleblu, an Iran analyst with the Foundation for Defense of Democracies, said the numbers Hook cited correlate with what many Iranian expatriates are hearing from friends and relatives in Iran.

Hook, who acknowledged that it is difficult to pinpoint the numbers, said the U.S. estimates came from crowdsourcing, intelligence and independent reports. He also said Iranians have sent the State Department 32,000 videos and photos documenting the carnage since Secretary of State Mike Pompeo appealed last month for them to do so.

The protests, which have spread to about 100 cities, began Nov. 15 after the government raised fuel prices. Many of the protesters have been young men from working-class cities and towns, who have demanded that Iran’s clerical leaders leave power. Iran’s rulers have blamed the unrest on “thugs” encouraged by Iranian opposition leaders in exile and foreign foes including the United States, Saudi Arabia and Israel.

In one video the State Department had received, Hook said, the Islamic Revolutionary Guard Corps can be seen firing on protesters who had blocked a road near the city of Mahshahr in southwest Iran. Several protesters were killed as others fled to nearby marshes, he said.

“The IRGC tracked them down and surrounded them with machine guns mounted on trucks” and began spraying them with bullets, he said.

“Between the rounds of ­machine-gun fire, the screams of the victims can be heard,” Hook said. “In this one incident alone, the regime murdered as many as 100 Iranians and possibly more. When it was over, the regime loaded the bodies into trucks.”

Hook said that when families tried to recover the bodies, the IRGC demanded they pay the cost of the ammunition and extracted their promise not to hold public funerals.

Hook called for the immediate release of all protesters who have been imprisoned in what he called “an environment that enables rape and murder,” as well as all political prisoners.

“Now is the time for all nations to stand with the Iranian people, diplomatically isolate the regime and sanction those officials who are responsible for murdering innocent Iranians,” he said.

Hook also showed a photograph of a missile painted blue and white that he said was part of a cache that a U.S. Navy ship seized on Nov. 25 from an unflagged ship off the coast of Yemen. He said that the weapons appear to be of Iranian origin and that the United States believes they were being delivered to Houthi rebels.

“This discovery is yet more proof of Iran’s efforts to inflame conflicts in the region by proliferating deadly weapons to its proxies,” he said. “It is also further evidence of how Iran repeatedly violates the U.N. arms embargo, which has been in place for over a decade.”

Western officials say the war in Yemen has pushed the Houthis, a Shiite fighting force that rose to power after the upheaval of the Arab Spring, closer to Iran.

The Trump administration has previously displayed weapons it says were either provided to or bound for the Houthis, seized in recent years by the United States or Persian Gulf allies, including sophisticated missiles officials say were assembled in Yemen.

Experts say the Houthis’ relationship with Iran dates back to 2009 during their clashes with the military of Saudi Arabia, the Shiite country’s primary regional rival.

The Wall Street Journal on Wednesday reported that U.S. military officials were considering adding 14,000 troops to the region. On Thursday, officials said the Pentagon was mulling a more modest troop increase of up to 7,000. It was not clear whether a decision on such a move was imminent.

Pentagon press secretary Alyssa Farah said the Pentagon is “constantly evaluating the threat situation around the world and considering our options.” But she denied there was a plan to deploy 14,000 additional troops.

The Pentagon has sent more troops, air defense systems and aircraft to the region in recent months amid heightened tensions with Iran. In June, President Trump approved and then called off strikes on Iran for the downing of a U.S. surveillance drone.

That incident was among recent assaults that the U.S. government has blamed on Iran, including attacks on commercial ships. As part of its response, the Pentagon is leading an international effort to patrol and surveil Middle Eastern shipping lanes that are key to global trade.

The Trump administration has depicted the Houthis as the next Hezbollah, the powerful Lebanese militia U.S. officials characterize as a virtual extension of Iran. But experts say the rebels remain nationalistic and relatively independent despite receiving Iranian assistance in recent years.

Also on Thursday, the State Department offered a reward of up to $15 million for information on Abdul Reza Shahla’i, a senior commander in the IRGC-Quds Force. Shahla’i is based in Yemen, said Hook, who cited his long history of plotting attacks on coalition forces in Iraq and providing explosives to Shiite militias.

Hook said the United States is concerned he may be involved in providing advanced weapons like the missiles seized by the Navy.

Louisa Loveluck contributed to this report.