Gains by Portugal’s governing Socialists in nationwide local elections on Sunday have strengthened the authority of José Sócrates, the prime minister, as he seeks to form a minority government following a general election two weeks earlier.

Aníbal Cavaco Silva, the country’s conservative president, on Monday formally invited Mr Sócrates to form a new government after his centre-left Socialists emerged from the general election as the single biggest party, but lost their overall majority in parliament.