CBS News cited Iranian sources saying up to 20,000 may have been killed, though only some 2,500 have been confirmed by the U.S.-based Human Rights Activists News Agency. Israel and Arab states have reportedly advised Washington that the regime is not weakened enough for a military strike to be decisive.

More than 12,000 people are feared dead in Iran after a sweeping crackdown on anti-regime protests, with CBS News reporting on Tuesday that sources inside and outside the country believe the toll could be as high as 20,000 and newly verified video showing hundreds of bodies stacked at a morgue near Tehran.

The outlet said the true scope of the bloodshed has been obscured by a near-total shutdown of internet and phone service imposed by Iran’s rulers over the past five days, with only limited outgoing calls allowing word of the killings to leak out.

Activist networks citing medical sources around the country told the network they now believe the death toll stands at a minimum of 12,000 and could reach 20,000, even as an unnamed Iranian official told Reuters some 2,000 people had been killed since the unrest erupted Dec. 28.

The U.S.-based Human Rights Activists News Agency said on Tuesday that it has confirmed 2,403 protester deaths, and that 18,434 people have been detained. HRANA also said that 1,134 people with severe injuries have been reported.

In one indication of the scale of the crackdown, CBS News reported it had verified video posted online Tuesday showing at least 366 and likely more than 400 bodies of slain protesters crammed into a morgue in a Tehran suburb, many bearing gunshot, shotgun and other severe wounds as relatives crowded around trying to identify them.

President Donald Trump on Tuesday urged Iranians to continue protesting and said that he has halted talks with regime officials.

Iran has warned neighboring countries that U.S. military bases on their soil would be targeted if Washington launches strikes over the protests, a senior Iranian official told Reuters on Wednesday, saying Tehran has urged states such as Saudi Arabia, the United Arab Emirates and Turkey to prevent any U.S. intervention.