Germany's domestic intelligence service has classified the popular Alternative for Germany party as "extremist," allowing for close surveillance of the group.

Days before a new government was due to be sworn in, German authorities classified the country's populist, far-right Alternative for Germany party an "extremist" goup that was actively working to undermine democracy.

Germany's domestic intelligence agency has formally designated the Alternative for Germany party as extremist, a move likely to further isolate the country's largest opposition party.