Europe’s antitrust regulator says they are “advancing” probes of Google’s ad business and Android operating system.

The commissioner, Margrethe Vestager, told The Wall Street Journal on Monday that regulators are looking at the links between the Android system and Google’s built-in applications. She declined to say when the investigation will wrap up.

{mosads}The regulator has also formally charged Google with giving preference to its own comparison shopping tool.

Separately, she told the European Parliament that “it is very difficult to make predictions” about when another investigation into Apple’s tax practices will be finished, Reuters reported.

Vestager’s comments come as she prepares to visit the United States this week. She will speak at an event hosted by the Women’s Competition Network in Washington, D.C., on Thursday and attend the spring meeting of the American Bar Association on Friday.

Since taking office in 2014, Vestager has pursued several American tech giants, including Google — now organized under parent company Alphabet, along with Apple and Amazon. That’s led to criticism that her office is unfairly targeting dominant American companies.

Even President Obama has weighed in on Europe’s agressiveness toward American tech companies, saying that in “defense of Google and Facebook, sometimes the European response here is more commercially driven than anything else.”

Vestager has denied any bias against American companies.

“Statistics on merger interventions also confirms that there is no geographical bias,” she said in October. “And these are the facts.”