Bomb blast on Colombia highway leaves at least 20 dead ahead of May elections

President blames dissident Farc faction for attack on Pan-American Highway that also injured 36 people in south-western region

The death toll in a weekend highway bombing in Colombia has risen to 20, with another 36 people injured, amid a surge of violence ahead of presidential elections next month.

Buses and vans were left mangled in the blast on Saturday on the Pan-American Highway, in the restive south-western Cauca department.