John Baird's office released a strongly worded letter it sent to Ban last week imploring him to stay away from the summit of the 120 Non Aligned Movement countries being held in Tehran.
Canada joined the U.S. and Israel in publicly condemning Ban's decision to attend the Iranian gathering, saying it would further the regime's "hateful purposes."
While many experts were unanimous in criticizing Ban for what they said was a bad political decision, others questioned whether Baird's stinging criticism had any impact at all.
Baird said Tehran will use Ban's presence at the meeting of more than 100 countries for its own propaganda.
"I just think they're going to exploit his presence there for nefarious purposes," Baird said Tuesday.
"We're concerned that his presence there will be used to bolster the regime politically. Obviously we wrote in strong terms to encourage him, like a number of our allies did, to reflect on that before he goes."
The minister noted Iran has pledged to destroy Israel and has an abysmal human-rights record.
Baird's letter to Ban last week outlined his concerns, which mirror those of Israel.
"Iran's current rulers will use your presence to further their own, hateful purposes. Such a visit would serve only to legitimize and condone the record of this regime, which Canada views as the single most significant risk to global peace and security today," says the Aug. 23 letter.
The West believes Iran is pursuing a nuclear weapons program, but Tehran denies the charge. It says it only wants to develop peaceful nuclear energy.
There has been growing speculation lately about a possible pre-emptive Israeli military strike that would target Iran's nuclear program.
The non-aligned movement is widely viewed as a Cold War anachronism, but Iran is playing up the gathering to elevate its battered, pariah-state image. Its foreign minister opened the week-long gathering with an appeal to rid to the world of nuclear weapons, despite concerns by the West that it is using peaceful nuclear technology as a cover to build weapons of mass destruction.
In addition to Ban, other high-profile attendees will include Indian Prime Minister Manmohan Singh, whose country buys Iranian oil, and Egypt's new president, Mohamed Morsi.
"No one should lend any legitimacy to a gathering convened in Tehran by this Iranian leadership in the name of non-alignment," Richard Haas, the president of the U.S. Council on Foreign Relations, argued in an analysis released Tuesday.
"It sends exactly the wrong message. We should be doing everything possible to isolate this Iranian leadership for its nuclear program, but also for what it's doing in Syria to facilitate the repression there."
Markus Gehring, a University of Ottawa international law expert, concurred, but was also critical of Baird's letter.
"It's pretty useless if it's a single country doing that. He would have done better co-ordinating his efforts with lots and lots of other countries."
Fen Hampson, director of Global Security of the Waterloo, Ont., Centre for International Governance Innovation, called Baird's letter "frothy" and questioned its effectiveness in light of Canada's historic loss of a temporary seat on the UN Security Council two years ago.
"It might have more bite had we been on that Security Council, quite frankly. We are an important donor to the organization but there'd be better vehicles for expressing that, on the Security Council."
Hillel Neuer, executive director of the Geneva-based non-governmental agency UN Watch, applauded Baird's initiative.
"It's not one of the great powers, but it is a moral voice. People listen to Canada," Neuer said in an interview from Geneva.
As Ban departed Tuesday, his office made no mention of Canada's objections, but noted the calls "from Israel and the U.S." to boycott the Tehran meeting. Ban pledged to talk to his hosts about terrorism, human rights, the crisis in Syria and Iran's nuclear program.
A spokesman said Ban would use his trip to convey the "clear concerns and expectations of the international community on the issues for which co-operation and progress are urgent for both regional stability and the welfare of the Iranian people."
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