Aliasghar Soltaniyeh, Iran's ambassador to the Vienna-based International Atomic Energy Agency (IAEA), told Reuters: "We will not, definitely, suspend again the enrichment."
Soltaniyeh spoke as six world powers were meeting in Berlin on Thursday to discuss their next steps on Iran, with Russia and China seeking assurances that force would not be used.
On Wednesday, the UN Security Council unanimously adopted a statement calling on Iran to freeze its uranium enrichment work, which can produce fuel for power plants or atom bombs.
It also asked the UN nuclear watchdog in Vienna to report in 30 days on Iranian co-operation with agency demands.
The council statement was the product of three weeks of negotiations among the five veto-wielding permanent members of the Security Council - Britain, France, China, Russia and the US. The final text was softened to remove language Moscow and Beijing feared could lead to punitive measures.
Oil held above $66 a barrel, in sight of its $70 record, after the UN statement.
Frank-Walter Steinmeier, the German foreign minister, said the Berlin talks should show the world speaking with one voice.
"For us it's about having the greatest possible unity in the international community. A similar meeting in London on January 31 achieved important progress," he told the Handelsblatt business daily.
Lavrov: Russia and China will not
tolerate the use of force
At the January 31 meeting, the five permanent members agreed to report Iran to the Security Council over its nuclear activities.
Manouchehr Mottaki, the Iranian foreign minister, speaking at the Geneva-based Conference on Disarmament, said that involving the council in Iran's nuclear case was "yet another indication of political manoeuvring by some Western countries".
Mottaki said the IAEA should be left to handle the dossier and criticised the council's demand for a report from the UN nuclear watchdog on Iranian compliance in 30 days as "nothing short of injustice, double standards and power politics".
He added: "This outcome would make it that much harder for us to actively pursue further initiatives and cooperation."
The Islamic republic says it only wants civilian nuclear power, not atomic bombs as the West believes.
Sergei Lavrov, the Russian foreign minister, said neither Moscow nor Beijing would tolerate the use of force against Iran. "Any ideas of resolving the matter by compulsion and force are extremely counter-productive," Interfax news agency quoted him as saying.
Qin Gang, China's Foreign Ministry spokesman, said Beijing believed a diplomatic solution remained possible.
"The [UN] statement is an international voice to the Iranians that they need to suspend their (uranium enrichment) activities, return to negotiations and that they continue to be isolated"
US secretary of state
Condoleezza Rice, the US secretary of state, said the world must keep up pressure on Iran.
"The presidential statement is an international voice to the Iranians that they need to suspend their (uranium enrichment) activities, return to negotiations and that they continue to be isolated," said Rice, who was en route to Berlin.
She urged the other permanent council members and Germany to take into account Iran's calls for Israel to be "wiped off the map", as well as its support for Syria and Hezbollah in Lebanon.
One EU diplomat said the US and EU diplomats would discuss with their Russian and Chinese colleagues a strategy outlined in a letter from John Sawers, a leading British diplomat, sent to his Western counterparts earlier this month.
Sawers said the non-binding presidential statement should be followed by a binding resolution based on Chapter VII of the UN charter, which deals with "action with respect to threats to peace".
Adoption of such a resolution would make compliance enforceable with economic sanctions or other measures.