Russia has begun “soil stabilization” work on the site of Phase 2 of the Bushehr Nuclear Power Plant in southern Iran, Russian state nuclear agency Rosatom has said.

"On 3 May 2018, soil stabilization works under the reactor building of power unit No 2 commenced at Bushehr-2 NPP construction site," the agency said on its website on Thursday.

"These works will ensure the performance of the most important stage of the project implementation - first concrete pouring planned for the third quarter of 2019," it said.

Soil stabilization is one of the preparatory stages for commencement of the nuclear power plant construction required to reduce the settlement of buildings and structures of the power plant and ensuring their stability in case of possible seismic impact.

Rosatom said the commencement of the works in the pit of the new power unit is planned in 2018. "All the works are being performed in accordance with the project implementation schedule," it said.

The construction of the power plant’s second and third phases began last November. It was reported at the time that the two phases would begin supplying electricity to Iran’s power grid in 10 years.

The first phase of Bushehr was connected to Iran's power grid in September 2011.

Rosatom said, "A successful experience of construction of the first power unit in Bushehr was the basis for expanding cooperation between the two countries in the field of nuclear power."

Russia and Iran signed a number of documents in November 2014, expanding cooperation in the field of peaceful use of atomic energy and opening the possibility of construction in Iran of up to eight power units.

The contract for construction of the second line of Bushehr NPP consists of two units of Russian design with a total capacity of 2,100 megawatts.

Russia is one of the signatories of the 2015 nuclear accord between Iran and world powers, the other parties to the contract being the United States, Britain, France, China, and Germany.

So far, the International Atomic Energy Agency, the United Nations nuclear watchdog, has invariably confirmed Iran’s commitment to the agreement.

US President Donald Trump has threatened on repeated occasions to sabotage the deal, and has said he would decide on May 12 whether to leave the deal and re-impose the sanctions.