The Federal Trade Commission said on Thursday it approved Google's proposed $3.1 billion purchase of advertising rival DoubleClick.

The deal, which combines Google's dominance in pay-per-click Internet advertising with DoubleClick's market-leading position in flashier display ads, is also being scrutinized by European antitrust officials.

In a 4-1 vote, the FTC decided to end its eight-month investigation of the transaction, concluding that the deal would not substantially lesson competition. Critics of the combination, first announced in April, had said it could give Google too much control over online advertising.

(Reporting by Diane Bartz, editing by Dave Zimmerman)