French group Publicis and Omnicom of the United States announced they had abandoned merger talks on what would have formed the world's largest advertising company, but markets shrugged off the news on Friday. In a joint statement the companies cited "difficulties in completing the transaction within a reasonable timeframe." The deal had been announced in July of last year. The boards of both companies approved the decision, they said. "The challenges that still remained to be overcome, in addition to the slow pace of progress, created a level of uncertainty detrimental to the interests of both groups and their employees, clients and shareholders," the statement said. Markets appeared unfazed by the announcement, with Publicis shares initially gaining nearly 1.5 percent in early trading in Paris. However they later stood down 1.0 percent at 60.09 euros while the Paris CAC 40 index was down 0.69 percent overall. The merged company would have been the world's biggest in advertising, with 130,000 employees and revenue of more than 20 billion euros ($28 billion). The Wall Street Journal reported last month the project had become a "battle of titans" between chief executives Maurice Levy of Publicis and John Wren of Omnicom Group. The project had been foreseen as being completed in early 2014. When delays emerged the two CEOs blamed regulatory and tax issues. But the Journal said it was a fight over power. The deal had been billed as a "merger of equals". But from a legal standpoint one company had to buy the other and neither was willing to be the acquired one, the Journal said. The two companies also disagreed on who would be the chief financial officer of the merged entity, the newspaper said. Levy said Friday that the companies had difficulties "building a good balance" between Publicis and Omnicom executives in the merged company. "We felt a great risk of a dilution of Publicis' model," he added. As it stands now, Omnicom is the world's second largest advertising company and Publicis is third. Number one is WPP of Britain. In 2013 Publicis posted record profits of 816 million euros, an increase of 11.5 percent from the previous year. Omnicom saw profits of $966 million, down one percent from 2012. Levy wrote in a note to Publicis employees that the merger with Omnicom "was never considered a necessity" but "a good opportunity". In an interview with BFM Business radio, Levy said that Publicis was not looking for another merger partner. "We will make acquisitions, we will develop ... invest in big data more massively than we had initially planned, we will make strategic choices that will lead us to modify the weight of our investments," said the Publicis chief executive. Levy, 72, told AFP he intends to stay on as the head of Publicis until his mandate expires at the end of 2015. "I don't feel weakened" by the collapse of the merger "even if I am extremely disappointed." Levy, who has headed Publicis since 1987, said he had the support of the company's board and was extremely happy with the team at the company. "If I had thought I had done something poorly, I could have decided to leave," he added.