(Reuters) - Aon reported a rise in first-quarter profit on Friday, powered by increases in interest earned from investments as well as funds held in a fiduciary capacity.

Interest income rose nearly six times to $28 million in the first quarter ended March, primarily due to interest earned on $5 billion investment of debt proceeds used to fund the purchase of NFP.

Last year, Aon agreed to buy privately held NFP in a deal valued at about $13.4 billion to tap the fast-growing middle-market segment of insurance brokerage, wealth management and retirement plan advisory.

Fiduciary investment income, which rose to $79 million in the quarter from $52 million a year ago, refers to interest earned on funds held in a fiduciary capacity by entities acting in a custodial role. These funds are typically held on behalf of policyholders, and the fiduciary has a legal obligation to manage them in the best interests of clients.

The U.S. Federal Reserve's higher-for-longer interest rate environment has helped such companies rake in higher income on funds and investments.

Last week, peer Marsh & McLennan also reported a better-than-expected first-quarter profit as fiduciary interest income rose 34% to $122 million.

Aon, which generates revenue through insurance, risk management services, consulting and advisory, reported adjusted net income attributable to shareholders of $1.13 billion, or $5.66 a share, for three months ended March 31, compared to $1.07 billion, or $5.17 a share, a year ago.

Revenue from commercial risk solutions unit rose about 2% to $1.81 billion, while that from reinsurance rose 8% to $1.17 billion.