Rights groups say hundreds of protesters have been killed in Iran as security forces violently suppress nationwide demonstrations, despite an imposed internet blackout.

The unrest poses a serious challenge to Iran’s decades-long clerical rule.

President Trump has warned of possible strong U.S. military action if more protesters are killed, while also saying a meeting with Iranian officials may be arranged.

Iran has threatened retaliation against U.S. and Israeli targets if attacked but has indicated it remains open to negotiations through existing channels, NPR has reported.

U.S. officials are expected to brief Trump on intervention options ranging from military and cyber actions to sanctions and support for protesters.