The United Nations is stressing that it is "impartial" in the presidential race of Mexico's July 1 elections, after one of its agencies said it would be willing to help the front-runner clean up government purchasing and other issues.

The campaign of leftist candidate Andres Manuel Lopez Obrador published a letter Friday from the U.N. Office for Project Services saying the agency would be glad to meet with Lopez Obrador after the election to plan assistance.

Lopez Obrador holds a commanding lead in most polls and wrote to the agency earlier asking for assistance in cleaning up Mexico's notorious contract corruption.

The deputy spokesman for the U.N. secretary-general issued a statement later Friday saying the agency's offer "should not be interpreted as an expression of support to any candidate."