AMSTERDAM, May 12 (Reuters) - Dutch insurer Aegon NV , reported on Thursday a better-than-expected 7% rise in first-quarter operating profit and said it was exploring a deal to reinsure its U.S. annuity portfolio -- which could lead to a large release of capital.

Aegon, which has significant operations in the United States, said operating profit was 463 million euros ($486 million) for the three months ended March 31, better than 428 million euros analysts had forecast in a company-compiled poll.

The improvement came in the United States, where adverse mortality claims in the company's individual life insurance business, mostly due to COVID-19, were $105 million, down from $157 million in the same period a year earlier.

On a call with reporters, Aegon's top executives said the company "will now actively go out and explore" a deal to reinsure its capital-intensive $80 billion U.S. variable annuity portfolio. The company has been working toward that possibility for several years, first by stopping selling the product, and later by improving its hedging.

Insurers are required to hold assets and set aside capital to pay variable annuities, which give pensioners some income for life -- and more if the underlying assets perform well. The insurers can cut the amount of capital they are required to hold against the annuities by having other insurance companies take over the downside and upside performance and longevity risks.

Analysts believe such a deal by Aegon could lead to a large release of capital for shareholders.

CFO Matt Rider confirmed that potential is the reason Aegon is exploring a deal, but said that "ultimately we have to engage with third parties to see if and what might be possible", including weighing counterparty risks on a deal of that size would bring. He declined to specify the size of the possible benefit the company hopes to obtain.

Separately, CEO Lard Friese said the company was confident of meeting its 2022 financial goals against a backdrop of rising inflation and interest rates.

In February ,the company set targets including generating 1.2 billion euros in operating capital for the year. It generated 318 million euros in the first quarter, up from 228 million in the first quarter of 2021.

In March, Aegon completed the sale of its Hungarian arm to Vienna Insurance Group (VIG), after a two-year delay over opposition by the Hungarian government to the sale as initially structured.

That led to a book gain of 372 million euros and an influx of cash, which helped the company launch a 300 million euro share buy-back programme.

Aegon shares were up 0.2% at 4.84 euros in early Amsterdam trading while the broader AEX index was down 2.3%.

($1 = 0.9517 euros) (Reporting by Toby Sterling; Editing by Mark Potter and Emelia Sithole-Matarise)