Mexico City ? Mexican police said Saturday they had broken up a vote-buying scheme in Chiapas on the eve of state elections, which will be closely watched in a country already straining under the turmoil of a disputed presidential election last month.

Four alleged supporters of Mexico’s leading leftist party were arrested Friday after authorities said they were caught trying to give away 36 tons of construction material to Hurricane Stan victims who promised to support the party’s gubernatorial candidate.

The suspects were charged with violating electoral laws, said Jose Domingo Perez, spokesman for the state attorney general’s office.

Aurora Guillen, a spokeswoman for the leftist Democratic Revolution Party, or PRD, said the party had no ties to the suspects and denied it was involved in vote buying.