LONDON (Reuters) - British Prime Minister Rishi Sunak said he feared the country's achievements in building a multi-ethnic, multi-faith democracy was being undermined, as he spoke out against a rise in extremism and criminality.

"In recent weeks and months, we've seen a shocking increase in extremist disruption and criminality," Sunak said in an address late on Friday outside his Downing Street office.

"We are a country where we love our neighbours, and we are building Britain together. But I fear that our great achievement in building the world's most successful multi-ethnic multi-faith democracy is being deliberately undermined."

(Reporting by Sachin Ravikumar and Alistair Smout; editing by James Davey)