They were shot dead by unidentified armed men, said the governor of the provincial town of Zahak where the incident took place.
Local security authorities are investigating the case, Jamshid Rakhshani further told Fars News Agency. No person or group has claimed responsibility for the deadly attack yet.
The Sistan-Baluchestan province has been the scene of a number of terrorist attacks in recent years.
On February 6, Jaish-ul-Adl terrorists kidnapped five Iranian border guards in the provincial Jakigour region and took them to the Pakistani territory.
In a message on April 6, Iran’s Interior Minister Abdolreza Rahmani Fazli said efforts by security and diplomatic bodies as well as locals had borne fruit and four of the abductees were freed and reunited with their families.
On October 25, 2013, Jaish-ul-Adl killed 14 Iranian border guards and wounded six others in a border region near the city of Saravan in the Sistan-Baluchestan province.
In February 2013, Iran and Pakistan signed a security agreement under which both countries are required to cooperate in preventing and combating organized crime, fighting terrorism and countering the activities that pose a threat to the national security of either country.
Iran has repeatedly called on Pakistan to comply with the terms of the agreement.