The European Union and Organization of American States both expressed alarm after Morales suddenly shot upward in the quick count Monday following a day-long pause in results.
Tensions rose when officials abruptly stopped releasing results from the official quick count of votes hours after the polls closed Sunday. The last numbers released before Monday night had showed Morales topping the eight other candidates, but also falling several percentage points short of the percentage needed to avoid the first runoff in his nearly 14 years in power.
Mesa, who stepped down as president in 2005 amid an outbreak of demonstrations led by Morales, then the leader of a coca growers union, called on citizens and civic groups "to conduct a battle in defence of the vote." The foreign ministries of Argentina, Brazil and Colombia also expressed concerns about the situation.