MEXICO CITY (Reuters) - The number of unsolved crimes in Mexico rose in 2015, with 93.7 percent of all infractions going unreported or uninvestigated, in a fresh blow to government efforts to stem years of drug violence and restore law and order.

The survey, published by the National Institute of Statistics and Geography (INEGI) on Tuesday, said the 2015 unsolved crime levels were up 0.9 percent from the year prior.

The 2015 figure was the highest since 2013, when the number of unsolved crimes reached 93.8 percent, INEGI said, and the second highest since the survey began in 2010.

The results of the poll come as the government struggles to stem a rising tide of murders, with 1,938 homicides across Mexico in August, the highest number since President Enrique Pena Nieto took office in 2012.

The government hopes a 2008 judicial reform, which sought to end behind-closed-doors trials and transition toward the more accountable oral legal system, will help lower the number of unsolved crimes.

But the reform's rollout across all of Mexico's states, which is scheduled to end this year, has so far been patchy.

More than 100,000 people have died in drug-related violence since 2007, and over 27,000 remain missing after having disappeared.

Crime and insecurity were estimated to cost Mexican households 236.8 billion pesos ($12.22 billion) a year, or 1.25 percent of the country's gross domestic product, INEGI found.

The survey showed that household spending on security measures increased by 17.7 percent in 2015, the largest rise since INEGI began examining security expenditures.

The survey also said 63 percent of those surveyed chose not to report crimes due to a distrust of authority.

The survey, carried out between March 1 and April 26, questioned 95,714 households.

(Reporting by Natalie Schachar and Gabriel Stargardter; Editing by Sandra Maler)