WASHINGTON / VIENNA  - US Secretary of State John Kerry warned Congress Wednesday that passing new sanctions against Iran would scuttle diplomatic efforts to rein in Tehran’s nuclear drive, although several lawmakers came away unconvinced.

“We now are negotiating, and the risk is that if Congress were to unilaterally move to raise sanctions, it could break faith with those negotiations and actually stop them and break them apart,” Kerry said.

Washington’s top diplomat spoke to reporters before beginning a closed-door meeting with members of a Senate banking panel, many of whom are skeptical of the White House’s request for a freeze on new sanctions. “The pitch was very unconvincing,” Republican Senator Mark Kirk said afterward.

Fellow Republican Bob Corker said Kerry made an “emotional appeal” but did not provide much-sought-after details of the proposal that Washington and other western powers put on the table for Iran.

“I was very disappointed in the presentation. It lacked content,” Corker said.

Democrat Tim Johnson, the Senate Banking Committee’s chairman, merely said he was “undecided” about whether to proceed with new sanctions.

Kerry emerged arm in arm with Vice President Joe Biden, who joined his fellow former senator in a briefing with senior Democrats after Kerry’s meeting with the banking panel, but neither of them spoke to reporters on the way out.

The House of Representatives has already passed legislation that toughens already-strict sanctions on Iran, whose economy by all accounts is reeling from the punitive action.

The banking panel is mulling new sanctions too, and some key members of President Barack Obama’s own Democratic Party back a tougher stance despite the diplomatic opening. “What we’re asking everybody to do is calm down, look hard at what can be achieved and what the realities are,” Kerry said.

“Let’s give them a few weeks, see if it works,” he said, adding that there was “unity” among the six powers negotiating with the Islamic republic. The so-called P5+1 — UN Security Council permanent members Britain, China, France, Russia and the United States, plus Germany — has contemplated offering relief to Iran on some economic sanctions in exchange for nuclear concessions.

“If this doesn’t work, we reserve the right to dial back up the sanctions,” Kerry said.

In that event Kerry said he would return to Capitol Hill “asking for increased sanctions. And we always reserve the military option.” Washington and Western allies allege Iran is trying to develop a nuclear weapon, a charge Tehran denies.

Iran halts expansion

of nuclear facilities

 Iran has not expanded its nuclear facilities in the last three months, a UN atomic watchdog report showed Thursday, in a possible confidence-building measure by Tehran before talks next week.

The International Atomic Energy Agency said that only four new uranium enrichment centrifuges were operating at Iran’s Natanz plant and no additional machines at the Fordo facility.

It also said that Iran has also not begun operating any new-generation IR-2M centrifuges and that “no ... major components” had been installed at a reactor being built at Arak.

The faster IR-2M centrifuges are of concern to the international community because in theory they shorten the time needed by Iran to produce enough weapons-grade uranium for a nuclear bomb.

The reactor at Arak is a worry because it could provide Iran with plutonium, an alternative to uranium for a nuclear weapon, once it has been up and running for 12-18 months.

The quarterly IAEA report, the first since President Hassan Rouhani took office in August, was released ahead of a new round of talks between Iran and world powers in Geneva next week.

Three gruelling days of talks that involved US Secretary of State John Kerry and other foreign ministers ended with no agreement in the early hours of Sunday morning.

The United States, China, Russia, Britain, France and Germany (the P5+1) want Iran to scale back the most sensitive parts of its nuclear programme.

In return Iran wants UN and Western sanctions that have been causing the Islamic republic considerable economic problems eased soon, and its “right” to enrich uranium recognised.

Obama has vowed he will not allow Tehran to develop an atomic arsenal. But last week’s Geneva talks between Iranian and western negotiators failed to reach an interim deal to halt its program.

Meanwhile Kerry warned that new sanctions could convince coalition partners to “bolt” from the negotiations because the United States was not a good-faith partner. Senate Republicans and Democrats alike bristled when the White House warned Tuesday that toughening sanctions could trigger a “march to war.”

The administration’s remarks marked a significant hardening of Obama’s stance towards Congress on sanctions as Washington prepares to resume talks with Iran on November 20.

As he entered the meeting, Kerry addressed criticism that negotiations failed in Geneva, saying Iran would have jumped at the interim deal if it was to their benefit.

“We have a pause because it’s a tough proposal, and people need to think about it, obviously,” Kerry said.