LAGOS (Reuters) - Nigeria's overnight rate spiked to 30 percent on Friday, up from 12 percent last week, after the central bank withdrew around 300 billion naira ($1.7 bln) from the system as part of efforts to support the naira, hit by falling oil prices. The central bank, which is trying to curb naira liquidity, last week hiked banks' cash reserve ratio for holding private sector bank deposits to 20 percent, from 15 percent previously. The bank also raised its benchmark interest rates by 1 percentage point to 13 percent and devalued the naira by 8 percent, as it sought to stem losses to its foreign reserves from defending the currency against weaker oil prices.