By Mateusz Rabiega, Jakob Van Calster

(Reuters) -Aegon plans to run a new 200 million euro ($224 million) share buyback in the second half of 2025, the Dutch insurer said on Friday, after higher than expected mortality in its main U.S. market hit quarterly capital generation.

The new buyback would supplement the ongoing 150 million euro repurchase programme that was 68% completed by March 31, Aegon said.

However, analysts at J.P. Morgan said in a research note that the combined value of the two buybacks at 350 million euros was below their forecast of 550 million euros.

The company's shares fell more than 2% in early trading.

Aegon's finance chief Duncan Russell told Reuters that it aimed to slim down its capital at hand to 1 billion euros by the end of 2026 through growth or via further shareholder returns.

At the end of the first quarter, Aegon held 1.6 billion euros of cash capital.

The Amsterdam-listed insurer, which has a large exposure to the U.S. through its Transamerica division, said its operating capital generation rose slightly to 267 million euros in the first quarter. That missed analysts' median consensus of 275 million euros compiled by Aegon.

Its Solvency II ratio, representing an insurer's ability to cover its liabilities, was 189% in the quarter, compared to analysts' forecast of 190%.

Russell said Aegon was looking into the mortality rate in the U.S., which was higher than it had projected, but tentatively mentioned a harsh flu season and statistical fluctuations as possible reasons for it.

"I do note that several of our peers have reported that it was quite an adverse flu season in the U.S., one of the more severe flu seasons in recent years," he said.

Aegon confirmed its guidance for the full year, including annual operating capital generation of around 1.2 billion euros.

($1 = 0.8922 euros)

(Reporting by Mateusz Rabiega and Jakob Van Calster in Gdansk, editing by Milla Nissi-Prussak)