The UN said "credible sources" had counted more than 400 strikes in the same period.
Observers say the vote, accompanied by a renewed crackdown on dissent, is meant to entrench the junta's power.
Voters in Myanmar's election say the poll is taking place in a "climate of fear", the BBC's South East Asia Correspondent Jonathan Head reports.
More than two dozen civilians were killed on Monday after a motorised army paraglider dropped bombs from above.
Critics have denounced the vote as a sham that will be used to entrench the military government's power.
"There is no income. Most people survive now by eating boiled taro roots," one person told the BBC.
It says the truce will be in effect from 2-22 April to speed up relief efforts after last week's deadly earthquake.
The quake comes at a time of ongoing civil war, food shortages and a declining economy.
Critics say the announcement is a sham designed to maintain the junta's power through proxy parties.
