Former FBI Director Robert Mueller, who made headlines as special counsel in an investigation into Russia's interference in the 2016 US presidential election, has died at 81, his family said.

"With deep sadness, we are sharing the news that Bob passed away last night," the family said in a statement on Saturday shared by The New York Times. "His family asks that their privacy be respected."

On his social media platform Truth Social, US President Donald Trump responded to Mueller’s death with the same contempt he showed the former federal prosecutor in life: "Robert Mueller just died. Good, I’m glad he’s dead. He can no longer hurt innocent people!"

Mueller had served as sixth director of the FBI from 2001 to 2013.

During his career as a prosecutor and FBI chief, Mueller displayed a patrician manner and sometimes wooden personality - just about the opposite of the bombastic Trump. He was known by some as "Bobby Three Sticks" because of his full name - Robert Mueller III - a moniker that belied his formal bearing and sober approach to law enforcement.

His Russia inquiry, detailed in a 448-page 2019 report, laid bare what Mueller and US intelligence agencies have described as a Russian campaign of hacking and propaganda to sow discord in the U.. denigrate 2016 Democratic presidential candidate Hillary Clinton and boost Trump, the Kremlin's preferred candidate. Russia denied election interference.