By Simon Clark

U.K. insurer Prudential PLC has taken a step back from the U.S. as it focuses on Asia, agreeing to sell a stake in its U.S. business to Athene Holding Ltd. for $500 million.

The investment from Athene, which is backed by New York buyout firm Apollo Global Management Inc., comes as Prudential prepares an initial public offering for its U.S. unit. The unit includes Jackson National Life Insurance Co. and asset-management firm PPM America Inc.

Athene also agreed to reinsure a $27.6 billion portfolio of Prudential's U.S. annuity liabilities.

"Prudential continues to prepare for a minority IPO of Jackson alongside the active evaluation of other options to create an independent U.S. business," the London-based insurer said Thursday.

Prudential said in August that its Asian operations were driving growth and that it would use third-party financing to expand its U.S. business. In October, the 172-year-old insurer spun off its giant U.K. fund-management unit M&G PLC.

Prudential Chief Executive Mike Wells said that the deal to sell an 11.1% minority stake in its U.S. business would enable investors to "benefit to the fullest extent possible from the opportunity presented by our Asia business" and "pursue a path for an independent Jackson."

Shareholders have been pushing for a breakup of Prudential. In February, activist hedge-fund firm Third Point LLC called on the British insurance firm to separate its U.S. and Asian operations, saying this would increase growth and drive value.

Third Point said in a February letter to Prudential's board that its Asian arm was "materially undervalued" by investors because it was tied to Jackson, which was "extremely complex to analyze."

Apollo is the largest shareholder in Bermuda-based Athene.

"Jackson has complementary distribution capabilities relative to Athene's business," Apollo co-founder Marc Rowan said.

Write to Simon Clark at simon.clark@wsj.com