Iran said Monday the "train has still not derailed" in negotiations aiming to restore the 2015 nuclear deal with world powers, despite new US sanctions on the Islamic republic.

The US on Thursday imposed sanctions on a network of Iranian petrochemical firms, as well as alleged front companies in China and the United Arab Emirates accused of helping Tehran to circumvent sanctions.

"We are still moving on the diplomatic path -- this train has still not derailed, despite the US reneging on its commitments and in spite of all of its actions," foreign ministry spokesman Saeed Khatibzadeh told reporters.

The Vienna talks, which began in April last year, aim to return the US to the nuclear deal, including through the lifting of sanctions on Iran, and to ensure Tehran's full compliance with its commitments.

But the ever-delicate dialogue has been stalled since March.

The 2015 agreement, formally known as the Joint Comprehensive Plan of Action or JCPOA, gave Iran sanctions relief in exchange for curbs on its nuclear programme to guarantee that Tehran could not develop a nuclear weapon -- something it has always denied wanting to do.

But in 2018, the US withdrew from the accord under then-president Donald Trump and reimposed heavy economic sanctions that prompted Iran to begin rolling back on its own commitments.

"We can certainly and quickly... finalise the agreement," Khatibzadeh said, if the US agrees to "put aside all the sanctions".

He also called on Washington to put an end to the so-called campaign of "maximum pressure" introduced by the Trump administration.

The United States has previously argued that Tehran's demand that Washington remove the powerful Revolutionary Guards from a terrorism blacklist is peripheral to discussions, although it can discuss the issue later.

On June 8, the International Atomic Energy Agency's Board of Governors adopted a resolution censuring Iran for failing to adequately explain the previous discovery of traces of enriched uranium at three sites which Tehran had not declared as having hosted nuclear activities.

On the same day, Tehran said it disconnected a number of IAEA cameras that had been monitoring its nuclear sites.

"The US decided again to prolong and delay the agreement and went to the (IAEA) board of governors meeting with the delusion of using leverage," Khatibzadeh said Monday.

"Of course, the response by Iran was a proportionate and decisive one," he added.