The defence ministry earlier said four had been killed.
The attackers had stormed a cultivated area and 'hacked' the farmers, the defence ministry said quoting a survivor who has been admitted to hospital.
Three soldiers were injured when another roadside bomb targeted an armoured vehicle in the same area.
The bus attack at around 7.40 am killed 26 and left more than 60 injured.
A truce between Sri Lanka and Tamil Tigers officially ends today, after the Sri Lanka government gave notice of its pullout two weeks ago.
All three attacks took place in the Moneragala district, which borders the Eastern Province of the island.
The government wrested control of most of the populated areas of the East, but Tamil Tigers are still active in remote forested areas.
The four farmers kille