Saudi Arabia's interior ministry said four people were executed on Monday for drug trafficking, including one woman, bringing to 53 the number of people put to death this year.

Two Pakistani men, a Yemeni man and a Nigerian woman were executed in the holy city of Makkah, the ministry said in statements carried by the official Saudi Press Agency.

Fifty-three people have been executed in the kingdom since the beginning of the year, according to a count based on official data released by SPA.

The ultra-conservative kingdom has one of the world's highest execution rates, with those convicted of terrorism, homicide, rape, armed robbery and drug trafficking facing the death penalty.

Rights experts have repeatedly raised concerns about the fairness of trials in the kingdom. The government says the death penalty is a deterrent for further crime.

Last year, Saudi Arabia carried out the death sentences of 120 people.