The prime minister offered that assessment of the growing tensions in the Persian Gulf during an interview Thursday on an Alberta radio program.
"Your listeners should be under no illusion, Iran is a very serious threat to international peace and security. In my judgment, it is the world's most serious threat to international peace and security," Harper said during an appearance on the Rutherford Show, an Alberta-wide radio call-in program.
Harper also said he has no doubt Iran wants a nuclear weapon and would be prepared to use one.
"This is a regime that wants to acquire nuclear weapons ... and has indicated some desire to actually use nuclear weapons," he said.
Harper's remark about Iran expressing a desire to use a nuclear weapon appears to fly in the face of the facts, said one expert.
"I think it would be an overstatement. To all intents and purposes, it looks like they're trying to acquire a nuclear weapons capability. But they have yet to cross the threshold," said Fen Hampson, director of the Norman Paterson School of International Affairs at Carleton University in Ottawa.
Iran maintains its nuclear program is meant solely for peaceful purposes, and has not admitted to pursing a weapon. Still, the international community, Canada included, believes the main goal is to build a nuclear bomb.
Iran has threatened to close the Strait of Hormuz, a key global oil passage, in possible retaliation for new economic sanctions aimed at curbing its nuclear ambitions.
Harper said the posturing over the Strait or Hormuz only underlines the degree to which Iran is "a serious threat."
Hampson agreed that is a serious issue.
"They (Iran) have been firing test missiles, and the United States is redeploying its Fifth Fleet to send a strong message to Iran," he said.
"The real danger in this kind of a situation is military activities — test firing of missiles and so forth — escalate. There's a miscalculation on one side, and it could well be the Iranians that take you into a real crisis."
Harper said Canada continues to work with its allies in imposing sanctions, and he said he believes they are having an impact.
"That's why the regime is lashing out from time to time."
Harper said Russia and China, which have opposed the censure or Iran for its nuclear program, have joined the international community and "appreciate that this is a serious threat."
"I think the problem is there's not a consensus about what to do about it precisely," Harper said.
On the Middle East's other flash point, Syria, Harper reiterated his government's desire to see President Bashar Assad step down.
The United Nations estimates 5,000 people have been killed in the anti-Assad uprising that began last winter.
"The violent repression is disgraceful, it's unacceptable and I don't think it's going to be successful over time."
Harper ruled out any international military intervention similar to the UN-sanctioned, NATO-led mission that supported the overthrow of Libyan dictator Moammar Gadhafi last year.
He said the Libya mission had the backing of the UN Security Council.
"That has not been forthcoming in this case," Harper noted, "and my own read of the situation is that Canada's principal allies would not be prepared to go to a military option in this case without such a resolution."