Mexican President Felipe Calderon on Saturday led a funeral service for his interior secretary Francisco Blake Mora, the victim of a helicopter crash investigators say was likely due to heavy fog. The 45-year-old Blake, a key figure in Mexico\'s war on drug cartels, was killed on Friday along with seven other people when their helicopter plummeted near the capital Mexico City. \"We say farewell today to Francisco Blake, one of my closest collaborators and a very dear friend,\" Calderon told mourners gathered at Campo Martes, a military base close to the Los Pinos presidential residence. \"His untimely death has deprived our country of a great human being... an honest and hard-working Mexican, a loyal patriot who was committed to the best causes,\" the president said. The ill-fated helicopter had taken off from Campo Martes on Friday to take Blake and his colleagues to a meeting of prosecutors in Cuernavaca, in the neighboring state of Morelos. At the funeral, the coffins of the eight victims were draped with Mexican flags. Pictures of the dead were placed in front of each coffin. Earlier in the day, Mexico\'s transport minister Dionisio Perez-Jacome told reporters that investigators believed poor visibility was probably behind the crash of the Super Puma aircraft made in France. \"According to the information available, there were layers of low-altitude fog and poor visibility\" along the projected flight path in the mountainous area, Perez-Jacome said. The chopper changed its route, presumably due to bad visibility, he said, adding that there was no indication in the wreckage of any damage from an explosion or fire. When asked about the possibility of foul play, Perez-Jacome said there was no evidence of \"anything other than an accident.\" US experts arrived in Mexico on Saturday to assist investigators as they pursue their probe, the minister said. A team from France was expected Sunday. Blake was the second interior secretary to die in an air accident during Calderon\'s presidency, after Juan Camilo Mourino perished in a small plane crash in Mexico City three years ago. Calderon canceled his trip to a weekend summit of Asia-Pacific leaders in Hawaii following Blake\'s death. US President Barack Obama \"reinforced his commitment to the close partnership between the United States and Mexico in this difficult time,\" in a telephone call with Calderon, the White House said. The United States supports Calderon\'s controversial crackdown on organized crime gangs involving tens of thousands of troops, which has been accompanied by a wave of violence which has left 45,000 people dead since 2006.