US firms Akin Gump Strauss Hauer & Feld and Cleary Gottlieb Steen & Hamilton have taken the lead roles on a $21.5bn (£13.5bn) tie-up which will create one of the world's biggest telecom companies.

Russian telecoms operator VimpelCom is set to acquire Weather Investments in the first quarter of 2011, handing the company a presence in 20 countries across the world.

Akin Gump is advising VimpelCom with a team led by London partner Dan Walsh alongside corporate partners Fred Heller, Pat Dooley and Sebastian Rice.

Cleary is acting for Weather Investments, fielding a team led by Paris corporate partners Pierre-Yves Chabert and Gamal Abouali.

Heller said: "The deal expands VimpelCom's emerging markets focus in Asia and Africa, and by adding Italy gives VimpelCom a strong foothold in developed markets where the potential for data growth is enormous – so the company will be positioned to take advantage of emerging market growth and also growth in developed markets."

VimpelCom covers Russia and the Ukraine, alongside other developing countries including Vietnam and Cambodia.

Weather Investments is the holding company for two Egyptian and one Italian operator that boast facilities in 10 markets in the Middle East, Africa and Asia.

The underwriters on the deal were UBS and Deutsche Bank for VimpelCom and Credit Suisse, Lazard Freres and EFG Hermes for Weather Investments.