Iran’s crackdown on nationwide protests continued Sunday, with reports of mass killings as demonstrations spread across the country amid warnings of drone surveillance.

The Center for Human Rights in Iran claimed a "massacre was unfolding," while the Human Rights Activists News Agency (HRANA) reported "surveillance drones flying overhead and movements by security forces around protest locations, indicating ongoing monitoring and security control."

"Drones are indispensable reconnaissance, surveillance and intelligence tools," military drone expert Cameron Chell told Fox News Digital. "They have given the Iranian government a distinctive upper hand in combating the protests."

"I doubt there will be any use of drones for direct strikes at this point," Chell said. "But I would not be surprised if, beyond surveillance, they were using drones to help position snipers and shock protesters."

"It does indicate the level of seriousness the government is applying towards the situation."

The full scale of the violence has been difficult to verify due to a near-total internet blackout. Iran’s connectivity to the outside world remained at roughly 1% of normal levels, according to NetBlocks.

The most conservative estimates indicate at least 2,000 people may have been killed across Iran over the past 48 hours, Iran International reported. 

The deaths of 544 people involved in the protests have been confirmed, with dozens of additional cases under review, according largest anti-regime demonstrations in years, according to analysts and opposition groups.

"We could see an escalation in the use of intimidation/force multiplier effect of drones and/or the use of tear gas or smoke to help create crowd disbursement," Chell said.

President Donald Trump renewed warnings to Tehran, saying the U.S. stands ready to support protesters and cautioned Iranian authorities against the use of lethal force.

"Iran is looking at FREEDOM, perhaps like never before. The USA stands ready to help!!! President DONALD J. TRUMP," he wrote on Truth Social.

Trump also said that protesters appear to be gaining ground in some cities and warned Iranian leaders not to begin shooting demonstrators, saying, "we’ll start shooting too."