MCI, the second-largest US long-distance telecommunications carrier, and Qwest Communications International, smallest of the four Baby Bell regional carriers, were in merger talks on Thursday that could lead to a deal.

Qwest is understood to have tabled an offer of about $6.3bn for MCI, executives close to the talks said. MCI, which has in effect been for sale since it emerged from Chapter 11 bankruptcy protection a year ago, is also believed to have held preliminary discussions with Verizon Communications, largest of the regional carriers.