Former national security adviser John Bolton said Friday a red line was crossed when Iranian-backed terrorists killed three U.S. soldiers with a drone strike Sunday in Jordan and called on the Biden administration to send a message by hitting targets inside the Islamic Republic.

The U.S. military on Friday began retaliatory strikes against Iranian proxies in Iraq and Syria in what is expected to be a series of attacks against Iranian targets, but Bolton told CBS News it won't be enough.

"I think all that is the right thing to do, but I don't think it will be enough," said Bolton, a former U.N. ambassador. "Looking at all the hostilities across the region, beginning with the Hamas attack on Israel, with the Houthi attacks on commercial traffic in the Red Sea, Hezbollah into northern Israel, and the Shia militia groups against Americans in Iraq and Syria, this is all at Iran's insistance.

"Throughout this entire period, Iran has paid no price for this. They look at their proxies as expendable. And until we make it clear to the mullahs in Tehran that we do not accept this kind of conduct by causing pain in Iran, it will continue."

Bolton expressed similar sentiment during an appearance Tuesday on Newsmax, when he said the U.S. "has to impose pain on Iran to reestablish deterrence."

"They have declared a red line against any targets inside their borders," Bolton told CBS. "They crossed an American red line by killing Americans. And until we cross their red line, they will not view this as a serious problem.

"I'm not saying this first attack should be regime-threatening; there are lots of targets inside Iran — Quds Force bases, air defense systems, and others — that would be a good thing to destroy and which would send a message. If the Iranian government doesn't get it, we can send more messages."

Bolton said he was surprised the Biden administration wasn't ready to retaliate immediately following the drone strike in Jordan because there have been more than 160 attacks on U.S. troops by Iranian proxies since the start of Israel's war against Iranian-backed Hamas terrorists in October.

"The trouble with the delay we've seen is that many of the Shia militia positions and Iranian positions in Syria and Iraq are not going to be today where they were last Sunday."

• Iran-Backed Militia Responds: 'Every Action Elicits a Reaction'
• Fred Fleitz to Newsmax: US May Not Get Reputation, Deterrence Back