Iran's parliament gave a partial nod to a nuclear deal with world powers Sunday but only after fiery clashes and allegations from a top negotiator that a lawmaker had threatened to kill him.

Ali Akbar Salehi, head of Iran's Atomic Energy Agency, went on the attack for the government at the end of a boisterous debate where he and other officials were accused of having capitulated.

Ultraconservative lawmakers repeatedly warned of holes in the text of the agreement and criticised President Hassan Rouhani for suggesting MPs were deliberately delaying the deal.

Red with anger, Alireza Zakani, who headed a panel reviewing the accord, known as the Joint Comprehensive Plan of Action, for two months, demanded "fundamental changes" to the text.

"This deal serves Wendy Sherman" and not Iran's interests, Zakani said, referring to America's senior negotiator in talks which resulted in the agreement in Vienna on July 14.

Hardliners in Tehran often railed against two years of diplomacy that led to the deal. Iran's government says the accord will protect the country's nuclear programme while seeing sanctions lifted.

Despite Sunday's disagreements, the outlines of a motion titled "Iran's Plan for Reciprocal and Proper Action in Implementing JCPOA" were approved by 139 of 253 lawmakers present.

One-hundred lawmakers voted against and 12 abstained. Iran has 290 MPs in total. They stopped short of endorsing the nuclear accord on Sunday and said specific details of the text are to be discussed and voted on Tuesday.

Members of the US Congress failed in September to torpedo the White House's historic deal with Iran.

Salehi, an atomic scientist by training and a former foreign minister, hit out at what he said was the "immoral" behaviour of some MPs in the way they had responded to talks and the deal.

Having to raise his voice, Salehi said: "Truth might be bitter for some... Listen. Listen. Hear me once and for all. Hear it from someone who is going be buried under cement."

The latter remark was in reference to a lawmaker who Salehi said took a vow to kill him because the government agreed to remove and disable the core of a reactor at Arak, one of Iran's nuclear sites.

"We negotiated within a framework and principles. Who set that framework? Me? A minimum and maximum was set for us," Salehi said.

So-called red lines for the talks were also laid down by Iran's supreme leader, Ayatollah Ali Khamenei, and the Supreme National Security Council that he oversees.

Foreign Minister Mohammad Javad Zarif, who led Iran's diplomacy with the six powers, attended Sunday's parliament session but he did not speak publicly.

State television broadcast only live audio of the session over stills of the parliament, citing "opposition from Majlis authorities".

However, pictures posted on social media sites showed the fierce exchanges.