Noor Rachmad told reporters outside the Nusakambangan prison in central Java that authorities have not decided when 10 other prisoners are set to be executed.
"It was not a pleasant thing to do but it was to implement the law," he told reporters.
"The executions are... aimed at stopping drug crimes."
Two Nigerians, one Senegalese and one Indonesian man were executed, the attorney general's office confirmed. Petitions to review their cases had been denied.
One of the Nigerians was Humphrey Jefferson Ejike, who was unjustly killed, according to his legal team.
"At this stage, we can only say that we are extremely disappointed with the fact that Jeff was executed," said Raynov Tumorang by text message. "The government does not respect the ongoing legal process on Jeff's case."
"There is strong evidence of torture and he was not given a fair trial. Racism towards our client can be seen in the court decision."
Cheikh Niang, Senegal's ambassador to Japan, who also oversees Indonesia, told CNN that the executed Senegalese prisoner was in fact from Nigeria but had traveled to Indonesia on a fake passport.
He said he visited the prisoner on March 15 and informed the Indonesian authorities.
Cries for end to more executions
Amnesty International said the 10 people still facing the death penalty include more Indonesians, a Pakistani, an Indian, a Zimbabwean, a South African and three Nigerians. Amnesty called the executions violations of Indonesian and international law.
Maryam Haq, the legal director of Justice Project in Pakistan, told CNN that a petition for clemency for Zulfikar Ali, the Pakistani man on death row, had been filed Friday.
"Any executions that are still to take place must be halted immediately. The injustice already done cannot be reversed, but there is still hope that it won't be compounded," said Rafendi Djamin, Amnesty International's director for South East Asia and the Pacific.
Before the executions took place, Indonesia's Foreign Ministry spokesman Armanatha Nasir stressed that capital punishment wasn't against international law.
"For Indonesia, the death penalty is a positive law that is still effective here, and it's not against human rights under the context of the 1945 constitution," he said.
"The action that Indonesia takes now is just about law implementation and enforcement. Just like how Indonesia respects the law of other nations, we hope all countries will respect Indonesian law."
Indonesian officials have said all measures will be taken to prevent the drama surrounding the executions in April last year
Australian drug convicts Andrew Chan and Myuran Sukumaran were executed after numerous appeals from supporters
who claimed they were reformed.
At the last moment Filipina Mary Jane Veloso, also sentenced to death, was spared. Indonesia apparently acceded to appeals to wait for a pending case against Veloso's alleged human traffickers in the Philippines.
Her lawyers said she was a victim of human trafficking and was tricked into carrying heroin in her suitcase.
Death in the dark
Executions in Indonesia usually take place late at night outside the Nusakambangan prison island in Cilacap, Central Java.
Inmates are given 72-hours' notice and are kept in isolation, with only the company of their religious counselors.
Veloso's sister told CNN that family are allowed to visit in the days before the execution, but afterward, the only confirmation they get the sentence has been carried out is the sound of gunfire in the distance.
Heavy rain on Thursday meant family members and lawyers on the island didn't hear any gun shots fired. Ricky Gunawan, a lawyer from the Jakarta Legal Aid Institute, said family members found out about the executions from news reports.
"No prosecutors, no one came out to explain what was happening," he said.
War on drugs
The Indonesian government insists the country faces a drug emergency that requires tough measures.
Its all-out war on illegal drugs has already seen a large number of executions in recent years.
Fourteen drug convicts faced the firing squad in 2015, six in January and another eight in April.
Under the administration of former President Susilo Bambang Yudhoyono, a total of 21 convicts were executed from 2005 to 2013.
United Nations Secretary-General, Ban Ki-moon appealed to Indonesia to halt the executions.
"Under international law, if the death penalty is to be used at all, it should only be imposed for the "most serious crimes," namely those involving intentional killing."
"Drug crimes are generally not considered to meet this threshold," the statement added.
Indonesia's prosecutors have always stressed that only death row convicts who have exhausted all legal avenues are put on the execution list. They are given the option to seek presidential clemency and a Supreme Court judicial review.