The US is offering a $5 million reward for information leading to the arrest of those behind the killing of Ecuadorean presidential candidate Fernando Villavicencio, Secretary of State Antony Blinken said on Thursday.

Villavicencio, a former lawmaker and crusading anti-corruption journalist, was gunned down in Quito on Aug. 9, less than two weeks before the presidential election. Ecuadorean police have arrested six suspects who they say are all Colombians belonging to criminal groups.

In addition to the $5 million reward, Blinken also announced a $1 million reward for information leading to the identification or location of any individual holding a key leadership position in the group responsible for Villavicencio's death.

"The United States will continue to support the people of Ecuador and work to bring to justice individuals who seek to undermine democratic processes through violent crime," Blinken said in a statement.