May 5 (Reuters) - Utility Ameren AEE.N on Tuesday reported about 23% higher first-quarter profit, driven by earnings from investments in infrastructure to improve reliability.

As power demand across the U.S. rises, utilities are ramping up spending on transmission and distribution networks, supporting steady growth in regulated, rate-based earnings.

Quarterly revenue for the electric segment rose about 2.4% to $1.66 billion, while gas-segment revenue climbed roughly 8.4% to $515 million.

Ameren said net income attributable to common shareholders rose to $357 million, or $1.28 per share, for the three months ended March 31, up from $289 million, or $1.07 per share, a year ago.

The St. Louis, Missouri-based company also reaffirmed its 2026 profit forecast of $5.25 to $5.45 per share.

Quarterly results were affected by lower electricity retail sales and higher interest expenses at the Missouri unit, as increased borrowing to fund infrastructure projects pushed up financing costs.

Ameren Missouri, the company's largest segment by profit, reported electric sales of 9,031 million kilowatt hours, compared with 9,421 million last year, due to a warmer-than-normal winter.

Ameren serves about 2.5 million electricity customers and more than 900,000 natural gas customers in a 64,000-square-mile area through its Ameren Missouri and Ameren Illinois rate-regulated utility subsidiaries.