NEW YORK—The PBN Company, a corporate and financial communications and public affairs firm with offices in Russia, Ukraine and the CIS, is merging with WPP sister agency Hill+Knowlton Strategies, which will now operate in Russia, Ukraine, Kazakhstan and throughout the CIS under the PBN Hill+Knowlton Strategies brand.

The merger comes after WPP acquired an additional 25.1 percent stake in The PBN Company. WPP had bought 49.9 percent of the company in 2007. The transaction creates WPP’s first majority-owned, full-service strategic communications firm in the region. PBN’s founders and top executives—Peter Necarsulmer, Susan Thurman and Myron Wasylyk—will retain a 25 percent ownership in the new company.

Jack Martin, global chairman and CEO of Hill+Knowlton cited PBN’s “depth of expertise and relationships with government, the business community and media” in the region, while Necarsulmer says that “increasingly our clients based in Russia, Ukraine and the CIS are requiring sophisticated, value-added strategic communications in priority markets around the world.”

PBN, initially founded in San Francisco, expanded into the former Soviet Union after handling public relations for the 1990 visit of then-President Mikhail Gorbachev to the Bay Area, and developed a business focused on crisis communications, government relations, financial communications and marketing communications for Western companies investing in the CIS and regional companies expanding internationally.

The firm’s clients include Abbott, Bank of America Merrill Lynch, BP, Citi, John Deere, Kingfisher, NYSE Euronext, Rosneft, Visa and Xerox, among others.