LONDON-- RSA Insurance Group PLC is selling its operations in the Baltics and Poland for GBP300 million ($503 million), the latest move by Chief Executive Stephen Hester to turn around the embattled insurer.

RSA, which issued a series of profit warnings last year amid problems at its Irish unit, is selling the divisions to Polish financial services company Powszechny Zaklad Ubezpieczen S.A. as part of its efforts to focus on the U.K. and other core markets.

The disposals follow a string of other recent changes at RSA. Since taking charge of the insurer in February, Mr. Hester, the former chief executive of Royal Bank of Scotland Group PLC, has launched a major fundraising and appointed new executives.

"These disposals are in line with our stated aim of focusing the group's geographical spread onto its core businesses in the U.K. & Ireland, Scandinavia, Canada and Latin America, and represent a good deal for our shareholders, customers and employees," Mr. Hester said.

The businesses being sold include Lietuvos Draudimas in Lithuania, AAS Balta in Latvia, the business of the Estonian branch of Codan Forsikring A/S and Link4 Towarzystwo Ubezpieczen Spolka Akcyjna in Poland.

On Wednesday, RSA said its U.K. chief, Adrian Brown , had agreed to resign after 25 years at the company after deciding he couldn't commit to the group's long-term turnaround plan.

News of Mr. Brown's departure came a day after the insurer appointed Paul Whittaker to the new role of group chief operating officer to lead the completion of its strategic disposals and support its remaining emerging-markets businesses.

Write to Rory Gallivan at rory.gallivan@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires