Indonesia has carried out the executions of four drug convicts, including three Nigerians.

The Indonesian man and three Nigerians were killed by firing squad shortly after midnight local time (17:00 GMT) at the Nusakambangan prison island.

A further 10 convicts who had been expected to be killed had a last-minute stay of execution.

Amnesty International condemned the killings as a "deplorable act" that violated local and international law.

Indonesia's Deputy Attorney-General Noor Rachmad said it was "not a pleasant thing but it was to implement the law".

"The executions are only aimed at halting drug crimes," he said, adding that the rest "will be carried out in stages".

Indonesia has some of the world's toughest drug laws, and has faced intense criticism internationally for resuming executions.

In April 2015, the execution of 14 drug convicts, mostly foreigners, was widely criticised.

Australia briefly withdrew its ambassador from Indonesia in protest over the execution of its citizens, Andrew Chan and Myuran Sukumaran.