SEOUL, South Korea - Sales at South Korea's top department and discount stores in December fell at a sharper pace than initially expected, marking a fourth straight month that sales at all stores declined, revised data from the trade ministry showed on Tuesday.

Combined sales last month at department stores run by Hyundai Department Store, Lotte Shopping and Shinsegae Co fell 0.9 percent in December from a year earlier, the trade ministry said.

This was slightly worse than a 0.3 percent fall estimated by the finance ministry earlier this month, but still an improvement from the sharp 6.5 percent drop in November.

The trade ministry attributed the poor sales to a drop in in-store clothing purchases due to consumers shopping more online, although robust foodstuff sales curbed the fall.

Sales at top discount stores dropped 3.8 percent last month from a year earlier, the same trade ministry data showed, slightly changed from an estimated 3.6 percent and versus a 4.7 percent decline in November.

Fewer working days at discount stores during the same period from a year earlier had eaten into sales, the revised data showed.

On a yearly basis, sales at department stores fell 0.7 percent in 2014, while those at discount stores dropped 3.4 percent.