CAIRO, Jan 6 (Reuters) - Egypt's pound slid by half a percent on Sunday at the central bank's fifth auction of foreign currency, with all $60 million on offer sold to banks at a cut-off price of 6.4185 pounds, the central bank said.

Thursday's cut-off price was 6.3860 pounds to the dollar. The weakening is in line with the central bank's interbank trading band, which it narrowed on Wednesday to plus or minus 0.5 percent from the previous 1.0 percent.

The central bank has sold $360 million and the currency has lost more than 4 percent of its value against the dollar since it began a new currency regime on Dec. 30 to slow the depletion of the country's foreign reserves, which the bank said had fallen to a critical level.