By Chijioke Ohuocha LAGOS (Reuters) - Nigeria's central bank has sacked top executives of Skye Bank over capital adequacy issues, a source with knowledge of the matter told Reuters on Monday. Chief Executive Timothy Oguntayo, who led Skye Bank to acquire nationalised lender Mainstreet Bank in 2014, resigned before a central bank announcement due later on Monday, the source added. Last year, the regulator gave three commercial banks until June 2016 to recapitalise after they failed to hit a minimum capital adequacy rate of 10 percent. "It's about capital adequacy," the source said. Skye Bank and Nigeria's central bank declined to comment. Skye Bank is designated as one of Nigeria's "systemically important" banks due to the size of total sector deposits it holds after the acquisition of Mainstreet Bank. This means it has to hold a higher amount of capital. Shares in Skye fell 9.5 percent to 0.95 naira. The lender has been in talks with shareholders and new investors to raise 30 billion naira ($150 million) after it suspended plans for a rights issue last year due to weak market conditions. (Additional reporting by Alexis Akwagyiram and Oludare Mayowa; Editing by Louise Heavens)