VIENNA (Reuters) - Iran decided not to escalate a stand-off over the extension of U.S. sanctions at a meeting of diplomats overseeing the nuclear deal it reached with world powers in 2015, senior Russian and Iranian diplomats said after the session on Tuesday.

Iran's top nuclear negotiator Abbas Araqchi leaves a hotel after meeting senior officials from the United States, Russia, China, Britain, Germany and France in Vienna, Austria, October 19, 2015. REUTERS/Heinz-Peter Bader

Tehran threatened last month to retaliate against a U.S. Senate vote to extend the Iran Sanctions Act (ISA), saying it violated the landmark agreement reached with six major powers under which the Islamic Republic curbed its disputed nuclear program in exchange for relief from international sanctions.

“Iran explained its concern on the extension of the Iran Sanctions Act ... as being an reintroduction of sanctions. I think the joint commission took Iran’s concern very seriously,” Abbas Araqchi, Iran’s top nuclear negotiator, told reporters.

When asked whether Iran used the meeting of the so-called Joint Commission to trigger a dispute resolution mechanism set out in the accord for cases where one participating country feels there is a breach of the deal, Araqchi said, “No.”

The bill extending U.S. sanctions against Iran for 10 years became law in December without President Barack Obama’s signature, but U.S. officials said its passage would not affect implementation of the nuclear accord. The European Union lifted all nuclear-related economic and financial sanctions on Iran.

The regular commission meeting on the nuclear deal took place 10 days before U.S. President-elect Donald Trump enters the White House amid great uncertainty about how he, as a fierce critic of a deal that Obama counts as a significant diplomatic achievement, will handle any future difficulties with Iran.

U.S. Secretary of State John Kerry said in December that he had renewed waivers of relevant sanctions, though he was not required to do so, “to convey to all stakeholders that the United States will continue to uphold our commitments”.

Alluding to these waivers, Araqchi said that participants in the Joint Commission meeting “insisted that this cessation of application should continue, otherwise it would be a significant non-performance of the (deal).”

Vladimir Voronkov, Moscow’s ambassador to U.N. missions in Vienna including the International Atomic Energy Agency, which is monitoring the deal’s implementation, said the ISA was “not a very favorable act, but life is life.

“The common approach from all the countries... was that it was necessary to do everything possible to avoid damage (to) implementation of the (nuclear deal),” he told reporters.