PARIS (Reuters) - Bouygues (>> Bouygues) said it did not plan to expand outside its three core telecoms, media and construction businesses, and added that if it were to sell its Alstom (>> Alstom) shares, it would use the cash to further develop those main divisions.

"It is the first time our three businesses have all, at the same time, promising prospects. We do not need to add a fourth or a fifth business," finance chief and deputy chief executive Philippe Marien told a group of reporters on Thursday.

"If we were sellers (of the Alstom shares), and I stress it is only an 'If', we would use these resources first to support our three businesses," he added.

The family-controlled Bouygues' group of businesses include construction and road-building, while it also owns France's biggest private TV broadcaster TF1 (>> TF1) as well as mobile phone operator Bouygues Telecom.

The construction business has been benefiting from large infrastructure projects in France and abroad, while increasing demand for mobile data and more content has boosted its telecoms and media businesses.

German industrial group Siemens (>> Siemens) and French rival Alstom agreed on Tuesday to merge their rail operations, creating a European champion to better withstand the international advance of China's state-owned CRRC Corp Ltd (>> CRRC Corp Ltd).

Bouygues is set to own 28.2 percent of Alstom as the French state has said it will not exercise an option to buy the 20 percent stake in Alstom which the government borrowed from Bouygues in 2014, when Alstom was selling its power engineering business to General Electric (>> General Electric Company).

As part of the Siemens-Alstom deal announced on Tuesday, Bouygues has committed to keep its Alstom stake until a shareholders meeting to formally approve the deal, or until July 31, 2018 at the latest.

Marien stressed that Bouygues had taken no decision at this stage on the future of its Alstom stake.

(Reporting by Dominique Vidalon and Gilles Guillaume; Editing by Sudip Kar-Gupta)

By Dominique Vidalon and Gilles Guillaume

Stocks treated in this article : Alstom, Bouygues, TF1, General Electric Company, Siemens, CRRC Corp Ltd