Carlos Slim, the Mexican billionaire who is the largest shareholder in MCI, has spoken out against the US telecoms group's $6.75bn (€5.1bn) merger with larger rival Verizon, almost three weeks after the deal was signed.

Slim, who owns 13.7% of MCI, formerly known as Worldcom, said both Verizon's offer and an $8bn alternative offer from Qwest, a rival, were too low.