With at least 90 per cent of the votes counted over the weekend, it was unclear if election watchdogs would immediately release the results -- and if the outcome would be recognised.
"We join the African Union and the international community in calling for calm as the Malawi Election Commission works to tally the vote and to resolve any challenges or complaints," State Department spokeswoman Marie Harf said in a statement.
"We urge all political leaders and their supporters to refrain from violence, and to resolve any disputes in a manner that adheres to Malawi's laws and its constitution."