Security forces and opposition supporters clashed after polls closed on Sunday at the end of a vote to choose the former French colony's first new leader in nearly four decades.
The diplomatic sources, who declined to be named, said three people had been shot dead in a neighbourhood near the airport in the capital Lome. No further details were immediately available and there was no immediate official confirmation of the deaths.
The International Red Cross said its workers had treated or transferred to hospital about 30 injured, seven of whom were seriously hurt, some with gunshot wounds.
Sunday's poll pitted Faure Gnassingbe, the 39-year-old son of former president Gnassingbe Eyadema, against a coalition of six opposition parties and effectively became a referendum on four decades of repressive rule by Eyadema's northern clan.
The election was meant to end a political crisis caused by
the death of Eyadema in February and the army's decision to name his son Gnassingbe as leader, which triggered violent street protests and an international outcry.
Gnassingbe finally agreed to step down at the end of February and called elections. Fears have been growing that the poll could trigger violence, and already both sides are alleging fraud ahead of the announcement of results.