"The chances now seem grim regarding sanctions that will be crippling," Ambassador Gabriela Shalev told reporters here.

She said Russia and China, two veto-wielding members of the UN Security Council, "are still looking to the diplomatic track" and appear reluctant to back a new round of tough sanctions proposed by Washington and its Western allies.

"The Chinese and the Russians still hope that diplomacy will work. They do not want to inflict any harm on the Iranian people," she added.

Shalev said that if the 15-member council was unable to agree on crippling sanctions, then Israel "will look to the countries themselves" to slap additional bilateral sanctions.

On Monday, Israeli Vice Prime Minister Silvan Shalom called on the Security Council to impose "crippling" sanctions on Iran over its nuclear defiance.

"The time has come to impose crippling sanctions on the Iranians and I asked to put the 300 leaders of the Revolutionary Guards that are controlling Iran these days on the (UN sanctions) blacklist," he told reporters after meeting with UN chief Ban Ki-moon.

Israel considers Iran its biggest security threat because of comments by President Mahmoud Ahmadinejad calling for the Jewish state to be wiped off the map and questioning the Holocaust.

Israel is widely reported to be the only nuclear-armed power in the Middle East, but it refuses to confirm or deny this, instead pursuing a policy of "nuclear ambiguity."

The UN Security Council has already slapped three rounds of sanctions on Iran over its refusal to halt uranium enrichment which Israel and the West view as a cover to build nuclear weapons.

Tehran denies the charge, saying the program is for peaceful nuclear energy.

The United States, Britain, France and Germany have proposed a fourth set of financial sanctions targeting Iran's powerful Revolutionary Guards, but China has questioned the usefulness of sanctions at this time.

Russia has signaled that it might be willing to back sanctions provided they only target Iran's nuclear proliferation activities.

Shalev said the world was edging closer to "two bad options": Iran continuing to race towards nuclear weapons capacity, which "will put the whole world under the threat of nuclear war," or Tehran being stopped only "by force."

She said the second possibility was currently being discussed by high-ranking US and Israeli political and military leaders, but declined to provide further details.

Brazil and Turkey, two non-permanent members of the Council, have expressed misgivings about new Iran sanctions.

On Tuesday, Turkish Prime Minister Recep Tayyip Erdogan signaled that Ankara might oppose new punitive measures.

"I don't believe that any further sanctions will yield results," Erdogan told reporters during a visit to Saudi Arabia, adding that two earlier rounds of sanctions "have never yielded results."

Turkey, which has good ties with its neighbour Iran, has offered to host an exchange of Iran's low-enriched uranium (LEU) for 20-percent-enriched uranium supplied by world powers to Tehran as part of a UN-drafted deal.

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