NEW YORK (Bloomberg) — Bermuda-based Assured Guaranty Ltd., the bond insurer stripped of the industry's last AAA ranking last month, said net income rose to $180.9 million in the third quarter, in part because it successfully forced mortgage bond sellers to buy back soured home loans.

Net income climbed to 96 cents a share, from a net loss of $35 million, or 22 cents a share, a year earlier, the company said last night in a statement. Operating income more than quadrupled to $222.8 million, or $1.19 per share. The average estimate of seven analysts in a Bloomberg survey was for operating income of 89 cents a share.

"Our strong operating earnings this quarter continued to reflect the stable results of our credit portfolio and the earnings power of our franchise," Dominic Frederico, chief executive officer of Assured, said in the statement.

Assured, backed by billionaire Wilbur Ross, is the only company left offering municipal-bond insurance after market leaders including MBIA Inc. and Ambac Financial Group Inc. had their credit ratings slashed because of losses linked to home mortgages.

Assured Guaranty climbed 63 cents, or 3.2 percent, to $20.37 in New York Stock Exchange composite trading as of 4:11 p.m. The shares have lost 6.4 percent this year. The company said in today's statement it increased its market share in the first three quarters of the year to 9.2 percent from 5.2 percent at the end of 2009.

Berkshire Hathaway Inc., which entered the municipal bond insurance market in late 2007, backed off after chairman Warren Buffett told investors in February 2009 that insuring municipal bonds appeared to have become "a dangerous business".

Macquarie Group Ltd. also plans to abandon efforts to start a municipal bond insurer, Moody's said in an October 25 report.

"Such a limited field raises questions about the sector's long-term relevance," Moody's analysts led by Ranjini Venkatesan wrote in the report.

S&P last month cut its financial strength and counterparty credit rating on Assured Guaranty Corp. and Assured Guaranty Municipal Corp. one level to AA+. The ratings firm cited the state of the financial guarantee market, which it said was "symptomatic of investors' and issuers' diminished demand for bond insurance."

Frederico called the downgrade an "unwarranted" action disruptive for his industry.

"We continue to request the establishment of a comprehensive regulator for the rating agencies to ensure a more stable and transparent business model and market for issuers and investors," he said.

The AAA ratings previously held by Assured's units were the last for any bond insurer. MBIA Inc. and Ambac Financial Group Inc. lost their top-level ratings in 2008 amid a housing crisis that saddled insurers with losses on mortgage-related bets.

Assured is gaining from efforts to get mortgage-loan originators to buy back loans it says were marketed for sale using faulty information. Assured said last month that originators have repurchased or agreed to buy back $412 million of loans, $111 million in the third quarter.

The company also sued affiliates of Deutsche Bank AG over $312 million of mortgage-backed securities the insurer guaranteed and says were "plagued by rampant fraud and misrepresentations".