The harsh words from Saeed Jalili came as Western calls mount for tough new punitive action against Iran over its suspect nuclear programme -- action that hinges on the approval of China, which wields a UN Security Council veto.
Beijing has until now refused to back Western calls for new sanctions, and earlier in the day again urged all parties to hold more talks and "show flexibility" in resolving the international standoff over Iran's atomic drive.
"Many issues came up in talks on which China accepted Iran's position," Jalili told reporters after talks with Chinese officials including Foreign Minister Yang Jiechi and State Councillor Dai Bingguo.
"We jointly emphasised during our talks that these sanctions tools have lost their effectiveness," Jalili said, though he said reporters "must ask China their position".
The Chinese foreign ministry was not immediately available to respond to Jalili's comments.
The envoy said the West should change their "erroneous methods" and stop "threatening" Iran, warning that the talks with six world powers including China and the United States could collapse if the West does not back off.
"If they continue with simultaneous talks and pressure, these negotiations cannot succeed," Jalili said.
"China as a large country can play an important role in changing these wrong methods."
Beijing has a close diplomatic and trade relationship with Iran, dominated by its imports of Iranian energy resources -- a point emphasised by Jalili, who said: "We believe China and Iran's friendly relations will continue."
US Ambassador to the UN Susan Rice said China was ready for "serious negotiations" on Iran -- a move hailed by the White House as an "important step" -- but the language used in Beijing did not signal any policy shift.
Yang said China "urges relevant parties to step up diplomatic efforts, and show flexibility, to create the conditions to resolve the Iranian nuclear issue through dialogue and negotiation," the foreign ministry said Friday.
The day before, ministry spokesman Qin Gang told reporters: "We have always and will continue to push for a peaceful settlement of this issue," adding that the crisis should be resolved by "diplomatic means".
Russia has also been reluctant to agree new sanctions but has taken a harder line on Iran's nuclear programme in recent weeks.
The United States and its allies suspect Iran is secretly trying to develop the atomic bomb, but Tehran says its nuclear drive is purely for civilian energy purposes, and that it has the right to nuclear technology.
Obama said earlier this week that he wants a fourth round of UN sanctions agreed upon within weeks.
In his rare hour-long call to Hu late Thursday from Air Force One, Obama "underscored the importance of working together to ensure that Iran lives up to its international obligations," the White House said.
Beijing and Washington have been at odds for months over a host of issues, but China signalled a reduction in tensions when it said Thursday that Hu would attend a nuclear security summit in Washington on April 12-13.
White House spokesman Bill Burton said Beijing's new readiness to enter the negotiations on Iran was "a very important step".
Obama "feels that we have been able to unite the global community in a way that it hasn't been united before in putting pressure on Iran," he added.
Source: AFP Global Edition