WASHINGTON, May 7 (Xinhua) -- A top adviser to World Bank President Paul Wolfowitz said on Monday that he will resign from his service, citing the controversy surrounding Wolfowitz made it difficult for him to be effective.

    "Kevin Kellems, Director of Strategy in External Affairs and Senior Adviser, has informed me of his intention to resign from service in the World Bank group, effective next week," said World Bank Senior Vice President Marwan Muasher.

    "Given the current environment surrounding the leadership of the World Bank Group, it is very difficult to be effective in helping to advance the mission of the institution," Kevin told the media.

    Kellems, once an adviser to Wolfowitz at the Pentagon, was promoted as senior adviser when Wolfowitz took over at the World Bank in 2005.

    Wolfowitz has apologized for the promotion and pay rises for Shaha Riza, who was a close female friend of Wolfowitz and once a staff member in the bank.

    Riza was removed to work with the U.S. State Department when Wolfowitz came to the Bank, to avoid any conflict of interest.

    While still on the World Bank payroll when she worked for the U.S. State Department, Riza was rapidly promoted and ended up with a tax-free salary package of about 193,000 dollars, even more than Secretary of State Condoleezza Rice receives before tax.