U.S. insurer AmTrust Financial Services on Thursday agreed to be acquired by a group of investors for a sweetened $2.95 billion deal that also helped secure the support of dissenting shareholder Carl Icahn.

Evergreen Parent, an entity formed by AmTrust's founding family, its chief executive officer and some private equity funds, will pay $14.75 per share in cash, up from its earlier offer of $13.50 per share, the insurer said.

Billionaire investor Icahn, who owns a 9.4 percent stake in the company, had strongly opposed the go-private deal and sued AmTrust and the controlling family, accusing them of trying to take the insurer private at the wrong time and the wrong price.

"By raising the merger price to $14.75, over $100 million of incremental value has been created for public stockholders," Icahn said on Thursday.

AmTrust's shares were up 2.7 percent at $14.48 in early trading, still trading below the latest offer.

The revised offer, however, failed to appease another shareholder opposed to the deal - Arca Capital. The firm reiterated that it sees $22 per share as the 'fair value' for AmTrust.

"We are still opposed to the $14.75/shr deal value - we think this still undervalues the company and it's still not enough," said Pavol Krúpa, chairman of the Czech-based investment firm told Reuters.

"The increased offer is just a cosmetic change to sway some shareholder's view."

Arca holds a 2.4 percent stake in the company. It said in a press release that AmTrust's long-term price target lies between $25 and $31, but it was ready to negotiate with the founding family.

"If no deal can be reached, we are very happy for AmTrust to remain public," Krúpa said.