Ban Ki-moon, the UN secretary general, is scheduled to visit Iran at the end of August to attend a summit of the Non-Aligned Movement, but his plans have subjected him to fierce criticism from the US and Israel.
The US and Israeli administrations explicitly asked Ban not to go as tension mounts over Iran's nuclear programme.
The West believes Iran is secretly developing nuclear weapons, and Israel has threatened to bomb the nuclear sites.
But others say the UN should be above US politics, or the interests of any particular country.
Pressure from the US and its allies kept Iran from attending a UN meeting on Syria, despite the wishes of special envoy Kofi Annan.
Al Jazeera's Kristen Saloomey reports from New York.