SAO PAULO, Aug 5 (Reuters) - Brazilian telecom Oi SA OIBR4.SA ended exclusive negotiations on Monday with Highline do Brasil, a portfolio company of U.S. private equity firm Digital Colony, for the sale of its mobile assets, a source familiar with the matter said.

Highline presented the best bid for Oi&aposs mobile unit on July 18, which had a minimum value established by the Brazilian telecom firm of 15 billion reais ($2.86 billion).

Four days later, however, telecoms operators TIM Participacoes TIMP3.SA , Telefonica Brasil SA VIVT4.SA and America Movil SAB de CV&aposs AMXL.MX Claro submitted a joint 16.5 billion reais ($3.15 billion) new bid for Oi&aposs mobile assets, higher than Highline&aposs offer.

Oi kept its exclusive talks with Highline after that, but decided to terminate it after Digital Colony&aposs portfolio company did not raise its bid for the mobile unit, the source said.

Highline has also presented bids for other two units of Oi. It has delivered a binding proposal to acquire Oi&aposs tower unit for 1.08 billion reais and also a non-binding offer for the company&aposs fiber unit.

It is unclear, however, how Oi will proceed now at the end of the exclusive talks with Highline. The telecoms companies had demanded from Oi the right to cover potential new bids by rivals. They also offer Oi a long-term contract to rent its telecom infrastructure.

Contrary to Highline, which has a small presence in Brazil, the telecoms firms would come under careful scrutiny as they are the top three players in the country.

Highline and Oi did not immediately comment on the matter.

Newspaper Valor Economico reported earlier on the end of Highline&aposs exclusive talks with Oi.

($1 = 5.2420 reais)