OTTAWA - Canada supports further sanctions on Iran, says Prime Minister Stephen Harper as he pledged to use his G8 presidency to stop Tehran's "worrying" nuclear ambitions.

"Canada will continue to work with our allies to find strong and viable solutions, including sanctions, to hold Iran to account," Harper said in a statement Wednesday.

"Canada will use its G8 presidency to continue to focus international attention and action on the Iranian regime."

Harper's remarks came after the Obama administration announced it was imposing new sanctions on several affiliates of Iran's Revolutionary Guard Corps. The measures target one individual and four companies for their alleged involvement in producing and spreading weapons of mass destruction.

The U.S. administration is pushing for additional international sanctions on Iran because of its decision to step up its uranium enrichment and its failure to prove that its nuclear ambitions are entirely peaceful.

The U.S. is lobbying the United Nations Security Council, which has already imposed a series of sanctions on Iran.

Harper called on Iran to immediately suspend its enrichment activity, and show "transparency and compliance" by stopping construction of new enrichment sites and co-operating with inspections by the International Atomic Energy Agency.

"Canada is deeply disturbed by Iran's decision further to enrich its nuclear material in defiance of UN Security Council resolutions. The regime's latest moves bring Iran considerably closer to possessing weapons-grade material," Harper said.

"Iran's past history of deliberately concealing aspects of its nuclear program makes this latest move even more worrying. Through its actions, Iran continues to test the resolve of the international community."

Harper also blasted Iran for its human-rights record, saying that Canada will "continue to voice our very serious concerns with the Iranian regime's stifling of democracy, its deplorable human-rights practices, and its negative implications for both regional and global stability."

Harper's comments came after France and Russia acknowledged that it was becoming necessary to discuss further sanctions on Iran.

The Canadian Press first reported last month that the Harper government wanted to feature nuclear non-proliferation as a major agenda item at June's summit of G8 leaders in Huntsville, Ont.

Allies are urging Canada to use the summit as an international platform to highlight the threats posed by the rogue nuclear states of Iran and North Korea, as well as terrorists acquiring the components for a so-called nuclear dirty bomb.

David Jacobson, the American ambassador to Canada, would not speculate Wednesday on whether the U.S. would ask Canada to join it in imposing sanctions on Iran if the idea is rejected by the UN.

"I think we're going to have to wait to see how that plays out."

Jacobson told an audience in Montreal that the Obama administration was unwavering in its commitment to global security but that Washington needs the help of its allies in Canada and elsewhere to keep the world safe.

"In dealing with those that break the rules, we must develop alternatives to violence that are tough enough to actually change behaviour. We're seeing that today -- literally today -- in Iran," the U.S. envoy told the Montreal Council on International Relations.

"For if we want lasting peace, then the words of the international community must mean something. Rogue actors that break the rules must be held accountable. Sanctions must extract a real price. Intransigence must be met with increased pressure and that pressure only exists if the world stands together as one."

Canada has downgraded its relations with Iran over the 2003 murder of Iranian-born Canadian photojournalist Zahra Kazemi, who was arrested and imprisoned in Tehran for taking photographs of a demonstration.

Kazemi was never charged with a crime, and died 17 days later in prison after being repeatedly beaten and sexually assaulted.

Her family in Montreal was waged an unsuccessful campaign to repatriate her body to Canada.