LONDON--WPP, the holding group that owns numerous PR firms, saw its public relations and public affairs revenues decline in the third quarter of this year.

On a like-for-like basis, PR and PA earnings dropped by 1.7 percent at the holding group, which owns the largest grouping of publicly-held PR firms, including Burson-Marsteller, Hill + Knowlton Strategies, Ogilvy PR and Cohn & Wolfe.

PR and PA reached £227m in the third quarter of this year, amounting to £686m in the first nine months of 2012 - the latter figure representing a 0.1 percent increase on the first three quarters of 2011.

In a statement, the group said that a decline in North American revenue across all of its PR/PA brands was to blame for the disappointing result, particularly in September. This was "only partly offset by strong growth in the United Kingdom, Latin America and Africa."

The group's prediction for the final quarter will also concern the PR industry, as it expects PR/PA revenue growth to "slow further" during the last three months of the year.

WPP's results come after Omnicom also reported a third-quarter decline in its public relations earnings.

On a constant currency basis, without excluding acquisitions and disposals, WPP's PR results look more encouraging, rising by 3.3 percent in the third quarter of this year.

In the first nine months of this year, WPP made PR/PA acquisitions and increased equity stakes in the US, Canada, the UK, Denmark, Finland, France, Russia and Australia.

Overall, group revenues rose by 1.9% to almost £2.5bn in Q3.