An international research institution says quickly evolving criminal gangs in Colombia are seeking to expand their influence in local elections this October and could reverse a decade-long trend of falling electoral violence.

The International Crisis Group issued its assessment in a report Monday. The Brussels-based organization says illegal armed groups seek to consolidate and expand their holds over local governments in October's gubernatorial, mayoral, departmental assembly and municipal council elections. The group also says the gangs are fast becoming larger, more robust criminal networks and some could develop a more ambitious political agenda.

The International Crisis Group says the government of President Juan Manuel Santos must rigorously implement measures to protect candidates and shield the electoral process against criminal infiltration, corruption and fraud. It describes the upcoming vote as the first electoral test for President Santos, who took office in August of last year.

Colombia has been mired in a nearly 50-year civil war involving the government, leftist rebels and rightist paramilitaries. The conflict has left thousands dead. Last month, President Santos signed legislation aimed at offering restitution to victims of the nation's violence.