Omnicom Group Inc, the largest U.S. advertising company, reported a better-than-expected 2.9 percent increase in revenue, helped mainly by growth in its international markets.

Omnicom's shares rose 4 percent in premarket trading on Tuesday.

The New York-based company, whose proposed $35.1 billion merger with France-based Publicis was cleared by EU regulators last month, reported a 4.3 percent rise in sales outside the United States.

Omnicom, home to agencies such as BBDO Worldwide and Goodby, Silverstein & Partners, said sales rose 3.2 percent in the United States, its biggest market.

The company's net income slipped to $300.5 million, or $1.13 per share, in the fourth quarter, from $307.1 million, or $1.13 per share, a year earlier.

Excluding merger expenses, Omnicom earned $1.18 per share.

Total revenue rose to $4.06 billion.

Analysts on average had expected earnings of $1.16 per share on revenue of $4.03 billion, according to Thomson Reuters I/B/E/S.