FedEx's net profit grew 7 percent to $610 million in its fiscal fourth quarter, the company announced Wednesday, but sagging results in key domestic business raised new concerns about a slowdown in shipping demand.

Domestic express volume slipped 1 percent and the profit engine in the trucking business slowed down, with operating income at FedEx Freight down 12 percent to $125 million despite an acquisition-led 28 percent boost in LTL revenue to $1.25 billion.

"The weakened industrial sector is currently limiting demand for transportation services, but we expect the U.S. economy to begin to show modest year-over-year improvement in the late summer to early fall timeframe," said Frederick W. Smith, FedEx chairman, president and CEO.

FedEx's overall revenue in the quarter ending May 31 was just short of $9.2 billion, up 8 percent over the year before. That gave the company $35.2 billion in revenue in the fiscal year, and a $2 billion net profit that was 12 percent ahead of the previous year.

The express operation that still makes up more than half of FedEx's business is slowing, growing only 4 percent in the fourth quarter, and the core U.S. domestic side is stagnant.

Domestic overnight box traffic fell 3 percent in the fourth quarter and the high-yield overnight envelopes were down 1 percent. Volume for second-day shipments grew, but a 2 percent decline in yield suggested competition on pricing was growing amid slack demand. By contrast, FedEx said International Priority revenue grew 7 percent.