NEW YORK—Omnicom Group has reported that revenues from its PR firms grew 1.5% in 2013, dragged down by a 3.7% drop in the fourth quarter of the year.

The fourth quarter performance by Omnicom's PR agencies, which include FleishmanHillard, Ketchum and Porter-Novelli, comes after the unit grew 3.4% in the first three quarters of the year.

On a reported basis, PR revenues droppped 2% to $340.8m in the fourth quarter of 2013. Excluding the impact of currency fluctuations and acquisitions, that amounts to a 3.7% decline. 

Omnicom's PR division was the only one of its four units to report a fourth quarter decline; advertising (+4.1%), CRM (+6.8%) and specialty communications (+2.5%) all grew.

For the year, Omnicom reported PR earnings of $1.3bn. Like its publicly-held peers, however, it did not break out the performance of individual agencies.

Last year, it was announced that Omnicom and Publicis Groupe are to merge, creating the world's largest holding company and the largest collection of PR operations. According to the results, Omnicom incurred $13.3m of pre-tax expenses in connection with the proposed merger during the fourth quarter of last year.

Overall, Omnicom Group reported a fourth quarter revenue increase of 2.9% to $4.1bn. PR acquistions during the fourth quarter of 2013 included Icon in Singapore and Californian government affairs consultancy Nunez LLC.