Like-for-like sales across the group, which also owns Darty France, fell by four per cent, with sales at Comet down 7.3 per cent.
Like-for-like sales at Darty fell 1.8 per cent, while total group sales were down 1.6 per cent between 1 November and 18 January.
Full year pre-tax profits would be at the lower end of expectations, the group said. However the figure would be an improvement on the previous year, the company said.
Despite the fall in like-for-like sales, which strip out the impact of sales at new stores, online sales across the group rose by 11 per cent.
And despite the sharp fall in Comet sales for the period, the UK chain posted "record trading between Boxing Day and New Year," Kesa said.
The company also said it had agreed a new credit facility worth 455m euros (£383m) on improved terms.
This would reduce interest payments by about 500,000 euros in the current financial year, and by about 3m euros in subsequent years, it estimated.
Kesa chief executive Thierry Falque-Pierrotin said: "Against a background of increased competitiveness, Darty France and the other established businesses delivered a robust performance, offset by softer trading at Comet and the developing businesses."