Saudi Arabia's nuclear research reactor is almost complete and the International Atomic Energy Association (IAEA) is discussing the necessary inspections with Riyadh, the head of the U.N. watchdog said on Wednesday.

Rafael Mariano Grossi said Argentine company Invap, which built the reactor, has finished the fuel and is going to ship it to Saudi Arabia.

"Of course there are a few regulatory aspects that need to be taken care of because from the moment Saudi has a research reactor, we will have to have a comprehensive safeguards agreement in place,” Grossi said, adding that Riyadh is getting close to signing an updated IAEA agreement from 2015.

Saudi Energy Minister Prince Abdulaziz bin Salman said in September the kingdom has decided to end light-touch oversight of its nuclear activities by the U.N. atomic watchdog and switch to full-blown safeguards, a change the agency has been demanding for years.

"I hope to be discussing with him (the Saudi energy minister) now so when we have the nuclear material here there will be the necessary inspections by the IAEA,” Grossi told reporters during a visit to Riyadh.

Asked when the fuel will arrive in Saudi Arabia, Grossi said: "It’s a decision by the Saudis... From a technical point of view, what I understand from the Argentine company is that they are ready.”

Saudi Arabia has a nascent nuclear programme that it wants to expand to eventually include activities like proliferation-sensitive uranium enrichment.

It is unclear where its ambitions end, since Crown Prince Mohammed bin Salman has said for years it will develop nuclear weapons if regional rival Iran does.

The IAEA is giving the kingdom "the advice that is necessary and indicating what is required from the inspection point of view from safeguards because these are sensitive technologies," he said.

(Reporting by Pesha Magid; writing by Aziz El Yaakoubi Editing by Alison Williams and Chizu Nomiyama)