ABUJA: Nigeria's naira dropped 1.2% to 493 per dollar, nearing a three-and-half year low on the black market, on Thursday.

The central bank has weakened its spot rate after moving to unify the currency's official rates with the traded market rates, traders said, effectively letting the naira weaken by 7.7%.

The black market rate weakened after the central bank on Tuesday abandoned its official rate of 380 naira, which it has held since July last year. The naira traded officially at 410 to the dollar on Thursday.

The naira hit 500 per dollar on the black market in November, a more than 3-1/2-year low.