The United States and its European allies welcomed new UN sanctions on Iran, but reminded Tehran that the door is still open to a diplomatic solution to the dispute over its nuclear ambitions.

Israel also hailed the latest punitive measures as an "important step" -- but Iranian leader Mahmoud Ahmadinejad dismissed them out of hand, comparing them to a handkerchief that ought to be "thrown in the dust bin".

Speaking at the White House, US President Barack Obama said the "toughest-ever" Security Council sanctions on the Islamic republic -- suspected of developing nuclear weapons -- sent an "unmistakable message".

"Today's vote demonstrates the growing costs that will come with Iranian intransigence," Obama said.

But he stressed: "I want to be clear, these sanctions do not close the door on diplomacy, Iran continues to have the opportunity to take a different and better path."

State Department spokesman spokesman Philip Crowley said Washington still planned to work with Turkey and Brazil on the Iranian question despite their opposition to the new sanctions.

"Clearly, we've had disagreement over specific tactics, but we will continue to work with Turkey, Brazil and other countries as we go through implementation of 1929," he said.

Twelve nations on the Security Council voted Wednesday in favour of a fourth set of sanctions on Iran, with Lebanon abstaining and Brazil and Turkey voting against, after Tehran defied earlier UN demands to halt uranium enrichment.

"These resolutions are not worth a dime for the Iranian nation," Ahmadinejad told the ISNA news agency in Tajikistan.

"I gave one of them (the world powers) a message that the resolutions you issue are like a used hanky which should be thrown in the dust bin. They are not capable of hurting Iranians."

Nevertheless, EU foreign affairs chief Catherine Ashton offered to meet Iran's top nuclear negotiator "at the earliest opportunity".

Her office in Brussels said in a statement that the Security Council resolution "keeps the door open for continued engagement" between the international powers and Iran.

"Sanctions are not the endgame or the final solution. They are part of a dual-track approach. We hope that today's decision will bring Iran to the negotiating table," the EU statement said.

In Israel, the sole if undeclared nuclear power in the Middle East, vice premier Silvan Shalomn told public radio shortly that the UN decision was "an important step in the right direction".

But Turkey worried that fresh sanctions will hinder, not help, the diplomatic effort.

"Turkey is worried that the UN Security Council's decision...will hurt diplomatic efforts and the window of opportunity for a peaceful settlement of the issue on Iran's nuclear programme," its foreign ministry said.

In London, British Foreign Secretary William Hague called the new sanctions "a very significant step forward".

"It really shows the international resolve on this issue. It shows that in a very broadly based way," he told reporters.

"And it shows that the Iranian tactic of simply not being willing to negotiate about its nuclear programme as a whole is not a tactic that is going to work."

German Chancellor Angela Merkel said she "strongly welcomed" the UN Security Council decision.

"Again and again and over a long period of time -- more than two years -- we gave Iran the opportunity to be transparent, including with the international atomic agency.

"Iran did not accept all these offers and therefore this resolution was needed ... I hope that the effect will be that Iran considers being more transparent and cooperative with international organisations."

Italian Foreign Minister Franco Frattini called the sanctions a "strong political signal" that the international community "cannot accept that Iran acquires nuclear weapons, embarking on a course of proliferation that would have serious effects on regional and global stability".

"The sanctions are not an end in themselves," but "should serve to bring Iran to the negotiation table".

Chinese state media said dialogue, negotiation and "other diplomatic means" were key to solving the stand-off.

China is a permanent, veto-wielding member of the UN Security Council and backed the UN measures but is keen to protect its substantial energy and economic interests in Iran.

Iran's atomic chief Ali Akbar Salehi, who oversees Iran's nuclear programme, lashed out at China, which has emerged as Iran's main trading partner in recent years, for agreeing to the sanctions.

"China is gradually losing its respectable position in the Islamic world and by the time it wakes up, it will be too late," Salehi told ISNA news agency.

"There was a time when China branded the US as a paper tiger. I wonder what we can call China for agreeing to this resolution."

Salehi also accused Beijing of "double standards" by taking a position towards "North Korea which has left the NPT different than with Iran which is a member of the NPT."

burs/gk/rom