WASHINGTON (REUTERS) - US President-elect Donald Trump on Thursday (Dec 15) raised more questions about Russia's reported role in cyber attacks on US political parties and individuals as well as the timing of the White House's response under President Barack Obama.

"If Russia, or some other entity, was hacking, why did the White House wait so long to act? Why did they only complain after Hillary lost?" Trump wrote in a post on Twitter.

Trump and his staff have repeatedly dismissed reports over the Russian hacking as "ridiculous," and said Democrats are upset that Trump won the Nov 8 presidential election over their candidate, Hillary Clinton.

In October, the US government formally accused Russia of a campaign of cyber attacks against US political organisations ahead of the election. Obama said he warned Russian President Vladimir Putin about consequences and last week ordered a review by the US intelligence agencies.

Meanwhile, NBC News reported late Thursday that US intelligence officials have "a high level of confidence" that Putin was personally involved in the Russian cyber campaign against the United States.

Russian Foreign Minister Sergei Lvarov told state TV channel Rossiya-24 that he was "dumbstruck" by the NBC report.

"I think this is just silly, and the futility of the attempt to convince somebody of this is absolutely obvious," he said.

The CIA has assessed that the attacks were aimed at helping Trump win the 2016 election, a position not endorsed by the Office of the Director of National Intelligence (ODNI) or the FBI, according to a senior US official.

The reports of Russian hacking have raised concerns among both political parties in Congress, with top Republicans breaking with Trump to call for closer scrutiny.

The US Senate Foreign Relations Committee plans a closed briefing and a public hearing on the matter in early January.