White Mountains Insurance Group Ltd. offered to pay 1.1 billion shekels ($308 million) for IDB Development Corp.’s 55 percent interest in Clal Insurance Enterprises Holdings Ltd.

The offer will expire unless accepted by 5 p.m. today in Tel Aviv, White Mountains said in a letter included in a regulatory filing yesterday. The transaction would have to be completed by May 31.

IDB Development Chairman Nochi Dankner is seeking to sell assets as the company struggles to pay creditors. White Mountains Chief Executive Officer Ray Barrette highlighted his ability to complete a transaction quickly. The company already has holdings including Sirius International Insurance Group and a majority stake in One Beacon Insurance Group.

“Our extensive experience in the insurance business and good relations with insurance regulators around the world make us a reliable party to close this transaction,” Barrette wrote.

White Mountains has $5 billion in capital, about $1 billion of which is immediately available for new investments, he wrote. The Hanover, New Hampshire-based company’s shares have advanced 8.7 percent this year.

IDB said yesterday that it had agreed to sell 32 percent of Clal to Hong Kong-based JT Capital Management Ltd. for about for 1.47 billion shekels. Dankner’s company faces a court deadline in Tel Aviv to sell a stake in Clal by today. An unidentified Thai investor withdrew an offer for the insurer last week.

Editors: Dan Reichl, Dan Kraut