A composite index of 25 major US metropolitan markets showed a 1.2% increase in house prices in April. Radar Logic's 25-MSA (metropolitan statistical area) RPX index showed the largest monthly increase since June 2007. The composite remains 20% below its year-ago level, however, and overall has plunged 32% below its peak. "The month-over-month increase in the Composite may mark the reemergence of seasonal price gains from February to June, which have not been seen since the onset of the housing bust," officials from the real estate data and analytics provider say in the report today. House prices across 18 major US metropolitan markets posted month-on-month gains in April, up from only 10 markets in the year-ago period. The Boston MSA posted the largest monthly gain in price, rising 8.1% over March to a total $181.78 per square foot (psf) -- the measurement used by Radar Logic to neutralize the effect of house size and location on house prices. Milwaukee followed at a 7.8% monthly gain to $115.86 psf. Each of the five California MSAs posted their largest monthly price gains since April 2005, according to Radar Logic. Las Vegas posted the steepest monthly decline of 6.1% to a total $81.28 psf, while Detroit fell into second place with a 4.7% monthly decline to $69.13 psf. Transaction counts in all MSAs fell 8% in April from the year-ago period, but on a monthly basis, transaction counts increased in 18 MSAs. Write to Diana Golobay.