The late Democratic icon Ted Kennedy's successor took office Thursday, formally giving US President Barack Obama's Republican foes the 41 Senate votes they need to be able to block his agenda.

"I want to get to work," Senator Scott Brown of Massachusetts told reporters moments after being sworn in. "There are urgent times for our nation."

Vice President Joe Biden, making a rare ceremonial visit to the US Senate, led Brown through his oath of office shortly after 5 pm (2200 GMT), after which Brown's new colleagues gave him a standing ovation.

Minutes later, Brown attacked Obama's policies, telling reporters at his first press conference as senators that an 800-billion-dollar economic stimulus package passed last year had "didn't create one new job."

And on Obama's top domestic priority, remaking US health care, Brown backed the Republican call to drop embattled Democratic legislation and "go back to the drawing board and start again."

Brown's shock victory in Massachusetts, seizing the seat Kennedy held for decades, sent Obama's Democrats reeling -- ending their 60-vote supermajority and fueling worries the November mid-term elections could be a rout.

Once a little-known state legislator, Brown has become a political superstar for Republicans dejected after suffering a thumping in the 2006 mid-terms and seeing Obama capture the White House in 2008.

"We look forward to welcoming him," Republican Senate Minority Leader Mitch McConnell said.

"Republicans look forward to having him join our conference. This was a high-profile election. Now it's time to get to work."

Brown's victory stripped Obama's Democrats of their already fragile 60-vote supermajority, enabling gleeful Republicans to stall legislation like the health care overhaul.

Brown, a moderate on social issues, said earlier he would be "an independent voter and thinker," and declared his top priority would be "jobs, jobs, jobs, jobs. Trying to figure out how we can get the economy moving again."