Citigroup Inc has substantially boosted its mortgage modification offers this month in response to the U.S. Treasury's call to speed the process and help prevent foreclosures, the bank's top mortgage executive said.

CitiMortgage in a report released on Tuesday also said it helped 108,000 homeowners avoid potential foreclosure last quarter, a rise of nearly 30 percent over the previous period as it ramped up participation in President Barack Obama's Home Affordable Modification Program, known as HAMP, to ease loan terms for up to 4 million borrowers.

CitiMortgage's latest report comes amid increased scrutiny of mortgage companies by the U.S. Treasury, which earlier this month said it would step up pressure on companies to quicken the pace of easing loan terms for eligible borrowers. It is seen as a key effort that could help stop home price declines and preserve a nascent rebound in U.S. housing.

CitiMortgage through July had started 27,571 trial modifications under HAMP, or about 15 percent of its eligible loans, the Treasury said on Aug. 4. That lagged the 20 percent achieved by competitor JPMorgan Chase & Co., but exceeded the 4 percent done by Bank of America Corp.

Based on the trends that I've been seeing in the month of August, I know that we are doing substantially better than that, Sanjiv Das, chief executive of CitiMortgage, said in an interview. We know that we are doing much better than the 15 percent.

CitiMortgage said it is the fourth largest U.S. mortgage servicing company.

Foreclosures are still on the rise despite signs that the U.S. housing is stabilizing from its worst downturn since the 1930s, raising concerns that burgeoning inventories could keep the broader economy in recession. Delinquencies are also on the upswing.

Disappointment over lender responses to HAMP led Treasury officials to set a goal of 500,000 modifications by November. Through July, modifications under the program had topped 200,000, the Treasury said earlier.

Citi was able to ramp up its modifications under HAMP after increasing its loss mitigation staff by about 45 percent since the start of the year, to 4,500, Das said.

My colleagues across the industry are driven by this same sense of urgency, Das said.

The percentage of borrowers that defaulted again after receiving a modification from CitiMortgage was 29 percent or less between the first quarters of 2008 and 2009, the report said. The rate improved for loans modified in the first quarter, it said.

Most modifications to meet HAMP objectives have been done with interest rate reductions or extended repayment periods, Das said. Only in extreme cases does a borrower need principal forbearance to achieve affordability, he said. (Editing by Leslie Adler)