UPDATE 1-Tax overhaul leads AmEx to first loss in 26 years, suspend buybacks

(Adds details on Tax charge, updates share movement)

Jan 18 (Reuters) - Credit card issuer American Express Co posted its first quarterly loss in 26 years and said it would not buy back shares for the next six months, both due to the impact of the recently enacted U.S. tax overhaul.

AmEx shares dropped 2.5 percent to $97.20 in trading after the bell on Thursday.

The company took a $2.6 billion charge to cover a new one-time repatriation tax on undistributed income of certain non-U.S. units and to adjust the value of its deferred tax assets and liabilities.

The charge lowered AmEx's capital ratios and to rebuild that, the company said it would suspend share buybacks for the first half of 2018, but continue paying dividends, though only at current levels.

Net loss attributable to common shareholders was $1.20 billion, or $1.41 per share, in the fourth quarter, compared with a profit of $825 million, or 88 cents per share, a year earlier.

Excluding the charge, AmEx earned $1.58 per share, beating analysts' estimates of $1.54 per share, according to Thomson Reuters I/B/E/S.

Total revenue, net of interest expense, rose to $8.84 billion from $8.02 billion last year as the company's customers spent more in the holiday season in the United States, its core market.

That also topped analysts' estimate of $8.72 billion. (Reporting by Pallavi Dewan in Bengaluru; Editing by Savio D'Souza)