By Barbara Plett
BBC News, UN
Iran says its nuclear programme is entirely peaceful
The UN envoys of six major powers have resumed negotiations in New York on a possible Iran sanctions resolution, bolstered by the nuclear summit held in Washington earlier this week.
They emerged from the meeting calling the talks constructive.
China's ambassador Li Baodong said the six now had a better understanding of each other's positions.
The French representative Gerard Araud declared they were getting into the substance of negotiations.
But diplomats say they are far from agreement on the strong new measures for which US President Barack Obama has called, despite the confidence he expressed after discussions with a key opponent of sanctions, Chinese President Hu Jintao.
Iran insists that its nuclear programme is for producing electricity, and does not have military aims, as Western states fear.
But it has defied five UN resolutions demanding that it stop enriching uranium.
Meeting on the sidelines of the Washington summit, foreign ministers of the six - America, Britain, France, Germany, China and Russia - endorsed the process of talks in New York, said a Western diplomat, but offered little guidance on specifics.
And the UN ambassadors were far apart when they presented opening positions at their first meeting last week, he said.
As expected, China and Russia want something "much much weaker, much much narrower" than that of the others, and they raised objections to "pretty much" everything.
China only recently agreed to talk about the draft after weeks of delay, and has not publicly said it would support sanctions.
The UN ambassadors are discussing a text prepared by the Americans outlining possible measures in five areas: energy, shipping, finance, an arms embargo and punishing members of Iran's Revolutionary Guard Corps, which oversees the country's nuclear programme, say diplomats.
Proposals include banning investments in the energy sector, tightening restrictions on banks and insurance, expanding limits on the arms trade to a full embargo, and increasing the list of individuals and companies facing travel bans and asset freezes, with a new focus on the Revolutionary Guards.
Afraid of endangering its extensive oil imports from Iran, China expressed concern about targeting the energy sector at talks last week, as did Russia, said UN diplomats.
Obama has been intensifying his efforts on Iran's nuclear work
Both countries are wary of damaging trade ties with Iran, and both have doubts that a new round of sanctions will succeed where others failed.
While neither want Iran to have nuclear weapons, their perception of the threat posed by its nuclear programme is different from that of the West.
Both are reluctant to expand beyond anything that focuses tightly on issues of proliferation, say UN diplomats.
There is also resistance to sweeping sanctions against the Revolutionary Guards.
"We're at the stage of objections being raised along the lines of, for example, you cannot just sanction a whole organisation that may have some legitimate activity," said one diplomat.
Western states would like to finalise the resolution by the end of April, but June looks more likely.
They had hoped the negotiations would not overlap with a review conference of the Nuclear Non-Proliferation Treaty (NPT) scheduled for May.
They fear Iran and its allies will use the event to lobby for support.
Tehran accuses the West of double standards, trying to sanction a signatory of the NPT without hard evidence that it has the bomb, while ignoring other states like Israel, Pakistan and India, which do have nuclear weapons and have not signed the NPT.
Iran, which says it is sending its foreign minister to the NPT Review Conference, has been pushing back against the rising pressure.
In a letter to the UN Security Council delivered late on Tuesday, Iran complained of what it called "nuclear blackmail" by the United States, questioning the intent of Washington's new nuclear policy.
Mr Obama excluded Iran and North Korea when he announced new limits on America's use of nuclear weapons last week.
Iran read this as an American threat to use nuclear weapons against the Islamic state.
The letter said this constituted a US violation of the UN Charter, posed a threat to international peace and security, and undermined the credibility of the NPT.