Former President George W. Bush said on Thursday that "there's pretty clear evidence that the Russians meddled" in the 2016 US presidential election, forcefully rebutting fellow Republican Donald Trump's denials of Moscow trying to affect the vote.

While never mentioning President Trump by name, Bush appeared to be pushing back on Trump's attempts to have warmer relations with Russia, as well as his comments on immigration.

The White House did not immediately comment on Bush's remarks.

"There's pretty clear evidence that the Russians meddled," Bush said at a talk in Abu Dhabi, the capital of the United Arab Emirates. "Whether they affected the outcome is another question."

Bush also said that "it's problematic that a foreign nation is involved in our election system. Our democracy is only as good as people trust the results."

US intelligence agencies have concluded Russia meddled in the 2016 election to help Trump win.

Numerous investigations are under way to determine whether Trump's campaign aided the Kremlin in its efforts.

Trump has repeatedly denied any "collusion" with Russia.

Bush spoke on Thursday at a summit in Abu Dhabi put on by the Milken Institute, an economic think tank based in California.

He made his comments while in a conversation with Michael Milken, known as the king of high-risk "junk" bonds in the 1980s. Milken pleaded guilty to securities-law violations in 1990 and served 22 months in prison. He agreed in a settlement with the SEC (US Securities and Exchange Commission) to a lifetime ban from the securities industry and paid a 200 million dollar fine.

Milken, who is a prostate cancer survivor, and his family have given hundreds of millions of dollars away in recent decades.