Shares of Bermuda bond insurer Assured Guaranty shot up by 20 percent on Friday, after the company announced its share of the US public projects business rocketed in the first quarter.

Assured, has benefited from being able to maintain its top credit ratings through a period in which most of its rivals saw theirs cut.

The company said that in the first three months of this year, it insured 426 US public finance new issue transactions, totalling $9.3 billion of par insured — a rise of 36 percent on the same period in 2008.

Assured's share of total US public finance new issue business rose to 11.1 percent from 8.1 percent last year.

"Our extensive due diligence and stringent underwriting standards exemplify our cautious approach to providing credit guaranties in the current environment," Bill Hogan, senior managing director of Assured's Public Finance Group.

"The transactions that we guarantee have met the highest underwriting standards, which utilise extensive economic stress-testing. Our guaranty of those bonds provides municipal bond investors with double-edged protection of both the investment grade underlying bond rating and Assured's financial strength and stability."

Many of Assured's bond insurer rivals have lost their triple-A ratings during the credit crisis, as a consequence of straying from their traditional business of guaranteeing municipal bonds and branching into the guarantee of financial instruments, some of which were backed by US residential mortgages.