Speaking at a hearing in Capitol Hill, FTC Chairman Joseph Simons said he had spoken on Tuesday with EU antitrust chief, Margrethe Vestager.

"We're going to read what the EU put out very closely," Simons told a subcommittee of the House of Representatives Energy and Commerce Committee.

In addition to the fine, equal to about two weeks' revenue, EU antitrust regulators ordered Google to stop using its Android mobile operating system to block rivals. The U.S. tech company said it would appeal.

Asked about the dominance of Google and Apple in the smartphone market, Simons said: "There is the two of them so they compete pretty heavily against each other."

He added that markets dominated by few companies are where antitrust enforcers often expect to find "problematic conduct."

The FTC had previously investigated Google for abusing its huge market share in web search, but ended the probe in early 2013 with a mild reprimand.

Also at the hearing on Wednesday, lawmakers from both political parties pressed the five agency commissioners to do more to stop robocallers and to ensure better security for sensitive data.

To tackle these and other issues, the commissioners - three Republicans and two Democrats - said the agency needed more resources and more authority, specifically the ability to create rules relatively quickly.

Simons and others also called for legislation to give the FTC the authority to seek civil penalties in the case of a data breach.

(Reporting by Diane Bartz; Editing by Bernadette Baum)