White Mountains Insurance Group Ltd. yesterday announced that its board of directors authorised the repurchase of up to an additional 600,000 common shares.

The authorisation is in addition to the company's existing one million share authorisation.

The 600,000 shares' market value is $179.5 million, based on the company's closing share price yesterday of $299.10.

As of July 31, 2010, the company had bought back roughly 840,000 common shares under the original authorisation approved in August 2006.

White Mountains chairman and CEO Ray Barrette said: "We continue to pursue many value enhancing opportunities, but at current prices we believe buying back shares is the best use of our undeployed capital for now."