An ambulance carrying the remains of an executed prisoner leaves the port of the prison island of Nusa Kambangan island, in Cilacap, Central Java, Indonesia, July 29, 2016. [Photo/Agencies]

CILACAP, Indonesia - Indonesia executed four convicted drug traffickers, including three Nigerians, early on Friday as it pushed ahead with its "war against drugs", although another 10 scheduled executions were delayed.

As many as 14 people were originally set to face the firing squad together on Friday, but officials decided a "comprehensive review" was needed to "avoid any mistake" in the 10 cases, Attorney General H. Muhammad Prasetyo said.

The date for the next round of executions has not been set, Prasetyo told reporters in Jakarta.

At least two prisoners among that group of 10, a Pakistani national and an Indonesian woman, have applied for presidential clemency, their representatives said. They said legal proceedings could take a long time.

Those executed - three Nigerians and an Indonesian man - were shot during a thunderstorm shortly after midnight on Nusakambangan Island in Central Java. The government ignored international calls for clemency and pushed ahead with its drive against narcotics.

"Our battle against drug crimes is not over and it will continue. We will maintain our commitment, our firmness and our consistency," Prasetyo said.

Indonesia has become a "business field" for the production, distribution, import and export of drugs, Prasetyo said.

Indonesia executed 14 prisoners, mostly foreign drugs offenders, just over a year ago, causing diplomatic outrage.

Rights activists and governments have again called on Indonesia to abolish the death penalty.

Those calls have gone unheeded and President Joko Widodo has said drugs pose as serious a threat as terrorism in what is one of Southeast Asia's biggest markets for narcotics.

The president's office often cites figures that drugs are killing at least 40 people a day, but several international experts have questioned the methodology used to arrive at those statistics.

The death penalty is widely accepted by the Indonesian public, but police had to break up a protest outside the prison on Thursday by members of a migrant workers group who called for mercy for the Indonesian woman who was scheduled to be executed.

Amnesty International called the latest executions "a deplorable act that violates international and Indonesian law" and pleaded that the other death sentences not be carried out.

Around 152 people remain on death row in Indonesia, including convicted drug traffickers from the Philippines, France and Britain, according to the Attorney General's Office.

Authorities plan to execute 16 prisoners this year and more than double that number in 2017.