US President-elect Joe Biden says a widespread data breach of the government allegedly carried out by Russia poses a "grave risk" to national security that cannot "go unanswered."

"This assault happened on Donald Trump's watch when he wasn't watching," says Joe Biden. (AP)

President-elect Joe Biden has said the perpetrators of a massive cyber-attack on the US government must face consequences and called out President Donald Trump over his response to the threat.

"We can't let this go unanswered," Biden said in pre-holiday remarks to the American people on Tuesday. 

"That means making clear and publicly who is responsible for the attack and taking meaningful steps to hold them in the account."

"This assault happened on Donald Trump's watch when he wasn't watching," Biden charged. "Rest assured that even if he does not take it seriously, I will."

"It is a grave risk and it continues. I see no evidence that it’s under control. I see none. Heard of none. Defense Department won't even brief us on many things. So I know of nothing that suggests it's under control," Biden said. 

The hacking spree uncovered last week breached at least half a dozen US government agencies and left thousands of American companies exposed. 

Secretary of State Mike Pompeo has said it appeared to have been carried out by the Russian government.

Biden's response to alleged Russian hacking 

The incoming White House chief of staff said on Sunday that Biden's response to the hacking campaign would go beyond sanctions. 

Ron Klain said Biden was mapping out ways to degrade the capacity of foreign actors to engage in cyber attacks against the United States.

Options being mulled by the Biden administration to punish Russia for its alleged role include financial penalties and retaliatory hacks on Russian infrastructure, people familiar with the matter have told Reuters news agency.

The Kremlin denies any role in the hacking.

"The question of the damage done remains to be determined. We have to look at, very closely, the nature of the breaches, how extensive they are, and what damage has been done," Biden said.

The cyber-attack is one of a mounting list of issues facing Biden when he starts work in the Oval Office, including fighting the coronavirus pandemic and the economic damage it has caused.

READ MORE: Trump: China not Russia may be behind cyber-attack

Biden addresses Covid bill

Biden also expressed empathy with struggling families and applauded Congress for passing the coronavirus relief bill as the nation deals with a Covid-19 surge that's casting a shadow over the Christmas holiday.

He called out to frontline workers, scientists, researchers, clinical trial participants, and those with deployed family members during the holiday season.

"Our hearts are always with you — keep the faith," he said in a year-end address from Wilmington, Delaware.

Noting the ways that the pandemic has altered his own holiday celebrations, which typically include up to two dozen relatives, Biden said, "not this year."

He said his administration will put forward another Covid-19 relief package next year, including a new round of stimulus payments.

He said a $900 billion relief package passed by Congress this week was a "first step" but that the government will have to do more. 

"Here is a simple truth: Our darkest days in the battle against COVID are ahead of us, not behind us," he said. 

READ MORE: Congress approves $900B Covid-19 relief bill, sending to Trump

Source: TRTWorld and agencies