BRUSSELS — The European Union’s antitrust regulator hit Alphabet Inc.’s GOOG, -1.22% GOOGL, -1.14% Google with its fourth round of formal charges in just over a year, cranking up pressure on the Silicon Valley company by threatening years of litigation on multiplying fronts.

The European Commission on Thursday issued a so-called statement of objections accusing Google of breaching EU antitrust rules by restricting how a website that offers a Google search function can show advertisements sold by other companies. At the same time, the EU also issued a supplementary charge sheet to boost its allegations last year that the U.S. technology firm uses its eponymous search engine to harm competitors of its comparison-shopping service.