(NewsNation) — Iran is rapidly approaching the capability to produce several nuclear weapons, putting it dangerously close to crossing a line it has flirted with for years, according to the former commander who oversaw the U.S. killing of a top Iranian general.

“Iran is very close to crossing that line,” Retired Gen. Kenneth F. McKenzie Jr., the former head of U.S. Central Command, said Monday on NewsNation’s “Elizabeth Vargas Reports”

Iran’s growing stockpile of highly enriched uranium has brought it within a small step of weapons-grade levels, according to a confidential report by the United Nations’ nuclear watchdog.

He said Iran not only has a rapidly growing uranium stockpile enriched to 60% — just short of what’s needed for nuclear arms — but has been seeking to perfect a warhead deliverable by missile as well.

The warning from the general echoes recent concerns from international inspectors about Iran’s nuclear work. Tehran has long insisted its atomic program is for peaceful purposes.

Just days ago, the U.N.’s International Atomic Energy Agency (IAEA) raised the alarm about Iran’s failure to cooperate and its growing highly enriched uranium stockpile.

This week, the U.S.’ European allies wanted to rebuke Iran at a special IAEA meeting. However, President Joe Biden’s administration hasn’t endorsed that approach so far, preferring to keep the possibility of reviving the 2015 nuclear deal open.

McKenzie said the U.S. needs to work closely with allies to confront the nuclear threat from Iran through economic sanctions, hindering its ability to secure needed weapon components and making clear the consequences of going ahead with a bomb.

Most importantly, he said, Washington must demonstrate its resolve.

“I think it’s just a continual business, and you have to approach it like that,” McKenzie said.

Consequences of killing Soleimani

McKenzie, who helped design and carry out the U.S. drone strike that killed Iranian General Qasem Soleimani in 2020, portrayed Soleimani as an extremely influential and irreplaceable figure for Iran.

He described Soleimani as a “magnetic” personality who was essentially the last word on matters and could unite Iraqi Shia militia groups under Iran’s control.

McKenzie believes the strike demonstrated U.S. resolve and willingness to act against Iran’s destabilizing activities in a way that had a deterrent effect despite Iran’s retaliatory missile attack on the Ain al-Asad airbase.

McKenzie is promoting a new book, “The Melting Point: High Command and War in the 21st Century,” which sheds light on the final days of the Afghan government and the Taliban takeover.