“I have allowed the Zambia Army, Zambia Air Force and Zambia National Service to help the Zambia Police in dealing with the security situation,” Mr Lungu said.
He said troops had already been deployed to some areas in the capital Lusaka and would be sent to other areas in the country “if the situation demands so”.
There have been incidents of violence by ruling party and opposition supporters across the country in the run-up to the vote.
The president cited the killing of two ruling party supporters in political violence in the capital, saying he would not allow that to be repeated elsewhere in the country.
The electoral body said it was investigating the incident and would take action against those found responsible.
The president is running for a second term in the elections.
His main opponent is Hakainde Hichilema who has unsuccessfully contested for the presidency five times.