UNITED NATIONS — After weeks of painstaking negotiations on the issue of Iran, unity on the Security Council threatens to fall apart as two council members have called for significant changes to a resolution proposed by the main powers.

Indonesia yesterday joined South Africa in proposing amendments that could unravel a package of mild sanctions agreed upon by the five permanent members and Germany. Indonesia wants the council to add a provision calling for a nuclear-free Middle East.

Along with the previous amendments proposed by South Africa, Indonesia’s addition — which is a reference to Israel’s nuclear capabilities — could unravel the council’s united front on Iran’s rejection of previous council resolutions.

Separately, Moscow officials yesterday denied issuing any “ultimatum” to Tehran, but the Associated Press reported that Russian nuclear technicians were withdrawn recently from Iran. The conflicting reports pointed to a possible new rift between Iran and Russia — as well as within Russia itself.

The assertion of power by council members representing poorer countries worries some in Washington. A former American ambassador to the United Nations, John Bolton, told The New York Sun yesterday that the so-called Nonaligned Movement maintained a caucus during the presidency of President George H.W. Bush, which consistently opposed measures by the big powers and complicated the council’s decision-making process.

“If this marks the re-emergence of this caucus at the Security Council, it is worrisome,” Mr. Bolton said, calling the amendments to the proposed resolution on Iran “not serious.”

On Monday, South Africa proposed a list of amendments to the draft resolution that Britain circulated last week among council members. It rejected the British proposal’s key new measures, which include a partial weapons embargo as well as restrictions on travel and financial transactions. South Africa also called for a three-month suspension of all sanctions that were imposed in the past against Iran.

China’s ambassador to the United Nations, Wang Guangya, said yesterday that “elements” of the Indonesian and South African proposals must be incorporated into the new resolution. But several European diplomats said none of the South African amendments are acceptable.

A Western diplomat, who spoke on condition of anonymity, said the five permanent members remained united on their proposal. “South Africa better think hard before it dissents,” he said.

Iran’s foreign minister, Manouchehr Mottaki, arrived in Cape Town yesterday for talks with President Mbeki, according to IRNA. A source familiar with Pretoria’s workings said South Africa’s ambassador to the International Atomic Energy Agency, Abdul Minty, the point man on diplomatic cooperation with Iran, drove the proposed amendments. South Africa’s main assertion in its proposal was that the council must “achieve a peaceful and negotiated solution” to Iran’s intransigence.

Skeptics say talks with Iran are bound to failure, a point that Mr. Bolton said might be demonstrated clearly once Iran’s President Ahmadinejad addresses the council late this week or early next.

“It would be very important to hear Ahmadinejad — especially for those who think Iran can be talked out of its pursuit of nuclear weapons diplomatically,” Mr. Bolton said.

Yesterday’s report of mass departures of Russian technicians from Iran followed another report claiming Moscow issued an ultimatum to Iran over a dispute over payments related to the nuclear plant in Bushehr. Russian and Iranian officials, however, denied both reports.

“There have been no Russian ultimatums to Iran of any kind,” Russia’s U.N. ambassador, Vitaly Churkin, told reporters yesterday. “Our deal with the Iranians is on track. It’s intact. It’s still there. We’re still working on it.”

But it was not clear everyone in Moscow follows that official line. “I believe that at RosAtom, the Russian atomic energy agency, they know exactly what Iran is doing, and they don’t want to be complicit in assisting in any way a nuclear weapons program,” Mr. Bolton said.

“It’s too bad that RosAtom and the foreign ministry don’t talk more often,” he said, adding that Russia’s President Putin also should consult more often with his own nuclear agency.