LONDON--Global multi-insurance firm RSA Insurance Group PLC Thursday called on shareholders for GBP775 million ($1.29 billion) to strengthen its balance sheet as it reported that its headline operating profit more than halved and canceled its dividend.

The troubled insurance firm, which sells personal motor and household insurance in the U.K. through its More Than brand, said that its weather charge will be 3.5% of premiums, significantly higher than the five-year average.

"RSA's 2013 results are poor and we need to grasp the nettles of both underperformance and undercapitalization," Chief Executive Stephen Hester said in his first earnings statement since his appointment.

"Together with a series of significant "self-help" measures, we believe this [rights issue] will put the group's capital in the right place for the future," Mr. Hester added.

Operating profit, a key measure in the insurance industry, was GBP286 million for the year ended Dec. 31, 2013, compared with GBP601 million in 2013, while net written premiums were unchanged at GBP8.66 billion.

RSA's IGD surplus, a regulatory measure that calculates surplus capital within the group, fell to GBP200 million, from GBP1.2 billion a year earlier

RSA recently appointed former Royal Bank of Scotland chief Stephen Hester as chief executive, replacing Simon Lee who resigned in December after a series of profit warnings over accounting issues at RSA Ireland.

RSA raised the alarm on potential problems in the Ireland business in November. A subsequent review by PricewaterhouseCoopers of the Irish claims and finance functions found signs of "inappropriate collaboration" in accounting by RSA's top executives. RSA said it would inject GBP135 million in capital to RSA Ireland and boosted the unit's reserves by GBP200 million.

Its shares closed Wednesday at 102 pence valuing the company at GBP3.76 billion.

Write to Ian Walker at ian.walker@wsj.com

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