Union Pacific and Norfolk Southern acknowledged Thursday that they were in merger talks that would create a single U.S railroad with rails stretching service from East to West Coasts. The Associated Press reported last week that the companies were discussing a tie-up but neither company confirmed until Thursday morning. The potential merger would combine the largest and smallest of the country’s six major freight railroads. There's widespread debate over whether such a merger would be approved by U.S. regulators, which have established a high bar for consolidation in the crucial industry.

THIS IS A BREAKING NEWS UPDATE. AP’s earlier story follows below.

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