The drills -- dubbed Eqtedar, or "might" in Farsi -- began last week and are set to continue until mid-March. They involve the army and the Islamic Revolutionary Guard Corps (IRGC), the ideological branch of Iran's military.

On Tuesday, the IRGC announced the drills were initially focused on the Natanz nuclear enrichment plant in central Iran.

"The exercises are currently being held at the Fordow and Khondab nuclear facilities," in central and western Iran respectively, state TV reported Sunday.

They involve missile and radar units, electronic warfare units, electronic intelligence and reconnaissance command carrying out "offensive and defensive missions", it said.

The military activities are taking place with Iran's nuclear programme under close watch ahead of US president-elect Donald Trump's return to the White House.

In his first term, Trump pulled the United States out of a 2015 nuclear deal with Tehran, and he also ordered the killing of a IRGC general in a drone strike in Iraq.

Iran is set to hold nuclear talks with France, Britain and Germany on January 13 in Switzerland.

In January, US news website Axios reported that White House national security adviser Jake Sullivan had presented President Joe Biden with options for a potential US strike on Iran's nuclear facilities if Tehran moved toward developing an atomic weapon before January 20, when Trump takes office.

Iran's foreign ministry spokesman Esmaeil Baqaei criticised the reports, saying threats against the country's nuclear facilities were "a gross violation of international law".

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

Iran has in recent years increased its manufacturing of enriched uranium, and it is the only non-nuclear weapons state to possess uranium enriched to 60 percent, the International Atomic Energy Agency (IAEA) nuclear watchdog says.

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