AmTrust Financial Services Inc. gained in New York trading Thursday after the insurer’s board approved the repurchase of as much as $150 million in shares following a stock slump last month.

The insurer rose 1.3 percent to $33.12 at 4 p.m.

The buyback plan is the company’s first since 2007 as Chief Executive Officer Barry Zyskind seeks to regain Wall Street’s confidence. AmTrust lost 22 percent in December after GeoInvesting, a website that provides research to subscribers, challenged the New York-based company’s accounting tied to its investment portfolio and insurance liabilities.

“Our future has never been brighter and our outlook is very positive,” Zyskind said in a Dec. 16 conference call held to respond to the stock’s decline. “We have never sold any shares and, on the contrary, have been buyers of the stock.”

AmTrust’s board in 2007 authorized repurchasing as many as 3 million shares. The company had bought back about 770,000 shares tied to that plan through the end of 2013, Elizabeth Malone, a spokeswoman, said in a telephone interview.

The timing and size of repurchases will be based on market conditions and liquidity needs, AmTrust said in a statement.