More than half of U.S. major cities showed an increase in foreclosures since the end of last year, according to RealtyTrac.

Mortgage servicers put a freeze on the process in 2010 to correct affidavit problems and resolve investigations from federal regulators and the state attorneys general. A $25 billion settlement approved in March brought new standards and relief requirements for struggling homeowners.

As servicers adjusted, foreclosures began to increase in different areas of the country during the first quarter.

Filings increased in 26 of 50 largest cities, led by Pittsburgh, where foreclosures jumped 49% from the previous three months.

Some cities still showed continued declines from the end of last year. Filings dropped 28% in Portland, Ore., and fell 26% in Las Vegas.

Servicers put Las Vegas filings on pause since a new state law took effect bringing new affidavit requirements and stronger enforcement for violations. As a result, Stockton, Calif., held the highest metro foreclosure rate in the first quarter, where one in every 60 homes received a filing.

Las Vegas dropped all the way to eighth on a 61% decline from the first three months of last year, but it wasn't the only city with filings well below year-ago levels.

Of the 50 major cities, 33 reported filings were down from the first quarter of 2011. Las Vegas showed the largest drop over that time, followed by a 53% decrease in Seattle and a 51% drop in Austin, Texas.

"First-quarter metro foreclosure trends were a mixed bag," said Brandon Moore, CEO of RealtyTrac. "While the majority of metro areas continued to show foreclosure activity down from a year ago, more than half reported increasing foreclosure activity from the previous quarter — an early sign that long-dormant foreclosures are coming out of hibernation in many local markets."