Separately, Aljazeera reports that Iran's supreme leader Ayatollah Ali Khamenei has said Iran will not give up its nuclear programme, and that UN sanctions cannot weaken the will of the people.
The US, which accuses Tehran of seeking to build nuclear weapons, reiterated that Iran may be referred to the UN Security Council. But Russia said dialogue was still the only way forward.
Scott McClellan, White House spokesman, said the international community had already warned Tehran that "the next step would be a referral" to the Security Council.
Wolfgang Schussel, the Austrian chancellor, said: "The possibility of ... sanctions continues to exist. But ... this should be a last resort."
Sergei Ivanov, the Russian foreign minister whose country has a veto in the Security Council, said the issue must be resolved by political means and under the International Atomic Energy Agency (IAEA)'s auspices.
Ivanov said: "On the whole I think that this problem ... must be resolved primarily within the political and diplomatic framework, and on the current stage, within the IAEA framework."
Russia talks suspended
Iran's announcement of a resumption on Monday coincided with the suspension of talks with Russia aimed at seeking a compromise over Iranian uranium enrichment, a key phase in the fuel cycle.
"There is no doubt that the Iranians are walking on the edge. And there is no doubt that when you walk on the edge, (treading on) the smallest stone can drop you in the abyss"
Israel's armed forces chief
Gholam Hossein Elham, a government spokesman, said on Monday: "Today, under the supervision of the agency, research activities will resume".
By agency, he was referring to the IAEA, the UN nuclear watchdog.
However, by late Monday there had been no announcement in Tehran of an actual resumption.
Meanwhile, Dan Halutz, Israel's armed forces chief, has said Iran is playing a dangerous game of brinksmanship with its continuing march towards developing nuclear weapons but it is not Israel's place to take action.
Halutz said on Monday: "There is no doubt that the Iranians are walking on the edge. And there is no doubt that when you walk on the edge, (treading on) the smallest stone can drop you in the abyss."
Iran has asked the IAEA to have inspectors ready to witness the removal of UN-supervised seals at its research centres, although as the suspension was voluntary, IAEA inspectors are not required to supervise the procedure.
But Hossein Entezami, spokesman for the National Security Council which is in charge of the nuclear file, said Iran was counting on the UN watchdog agency's co-operation to resume its research.
ElBaradei is losing patience
with Iran's lack of transparency
He said: "I hope that the agency (IAEA) will do the necessary so that the research activities resume today."
Mohamed ElBaradei, the IAEA's chief ,said on Monday he was "losing patience" with what he called Iran's lack of transparency.
He said: "There are still a number of important issues where I have not been able to make progress and I still need very much Iran's transparency and Iran's active cooperation."
Europe has warned that the move, which would end a two-year suspension, would jeopardise any resumption of wider talks on ending the crisis with the West over Iran's nuclear activities.
Germany, which along with Britain and France makes up the EU troika leading negotiations with Iran, warned that the decision "cannot remain without consequence".
Steinmeier has accused Iran of
breaching its commitments
Frank-Walter Steinmeier, Germany's foreign minister, said: "This marks a breach of Tehran's commitments."
And his French counterpart, Philippe Douste-Blazy, urged Iran "to immediately and unconditionally reverse its decision".
But Iran's supreme leader Ayatollah Ali Khamenei voiced defiance, saying Tehran would not give up its nuclear programme.
Khamenei said: "The Islamic Republic of Iran will not give up its undeniable rights to peaceful nuclear technology, which has been achieved by the talented youth of the country.
"The ones who are invoking sanctions have sanctioned Iran whenever they could ... such sanctions have no effect."
Iran has been trying to draw a distinction between research into the fuel cycle and actual production of enriched uranium, which can be used as fuel in civil reactors or, in highly enriched form, as the explosive core of an atom bomb.