They are the second round of talks over Iran's nuclear programme in less than two months, following a discreet meeting held in Geneva, Switzerland, in November between Tehran and the three European powers, known as the E3.

"These are not negotiations," the German foreign ministry told AFP. Iran has similarly emphasised that the talks are merely "consultations".

The meeting is a sign that the E3 countries "are continuing to work towards a diplomatic solution to the Iranian nuclear program, the progress of which is extremely problematic," the French foreign ministry said on Thursday.

Monday's meeting comes as Iran's nuclear programme received renewed focus in light of Trump's imminent return to the White House on January 20.

During his first term, Trump had pursued a policy of "maximum pressure", withdrawing the US from a landmark nuclear deal which imposed curbs on Iran's nuclear programme in return for sanctions relief.

Tehran adhered to the deal until Washington's withdrawal, but then began rolling back its commitments.

Efforts to revive the 2015 nuclear pact have since faltered and European officials have repeatedly expressed frustrations over Tehran's non-compliance.

- 'Breaking point' -

Last week, French President Emmanuel Macron said the acceleration of Iran's nuclear programme is "bringing us very close to the breaking point". Iran later blasted the comments as "baseless" and "deceitful".

In December, Britain, Germany and France accused Tehran of growing its stockpile of high enriched uranium to "unprecedented levels" without "any credible civilian justification."

"We reiterate our determination to use all diplomatic tools to prevent Iran from acquiring a nuclear weapon, including using snapback if necessary," they added.

The snapback mechanism -- part of the 2015 deal, known as the Joint Comprehensive Plan of Action (JCPOA)-- allows signatories to reimpose United Nations sanctions on Iran in cases of the "significant non-performance" of commitments.

The option to trigger the mechanism expires in October this year, adding urgency to the ongoing diplomatic efforts.

The International Atomic Energy Agency (IAEA) nuclear watchdog says Iran has increased its manufacturing of enriched uranium such that it is the only non-nuclear weapons state to possess uranium enriched to 60 percent.

That level is well on the way to the 90 percent required for an atomic bomb.

Iran maintains that its nuclear programme is solely for peaceful purposes and denies any intention to develop atomic weapons.

It has also repeatedly expressed willingness to revive the deal.

President Masoud Pezeshkian, who took office in July, has favoured reviving that agreement and called for ending his country's isolation.

In a recent interview with China's CCTV, foreign minister Abbas Araghchi also expressed willingness "to engage in constructive negotiations".

"The formula that we believe in is the same as the previous JCPOA formula, namely, building trust on Iran's nuclear program in exchange for lifting sanctions," he added.