The executions — typically carried out by public beheading — bring to 114 the number this year, compared with 87 for all of 2014, according to AFP tallies.
Read: Saudi beheads murderer in 110th execution since January
Ethiopians Argawi Aldo Heilan Meriam and Hadish Zel Alam had been convicted of beating a fellow countryman to death and robbing him, the interior ministry said in a statement carried by the Saudi Press Agency.
They were put to death in the southwestern Jazan region, it said.
In a separate case, Pakistani Esmat Sharif, found guilty of smuggling heroin hidden in his body, was executed in Jeddah, the ministry said.
The fourth condemned man, Saudi Mushasha Harisi, was executed in Jazan after his conviction for shooting dead another Saudi in a dispute, the ministry said.
The number of Saudis and foreigners put to death so far in 2015 is up 131 percent on the figure for all of 2014, according to AFP tallies.
"Saudi authorities have been on a campaign of death this year," Sarah Leah Whitson, Middle East and North Africa director of Human Rights Watch, said in June when the number of executions had already exceeded last year's total.
Under the conservative kingdom's strict Islamic sharia legal code, drug trafficking, rape, murder, armed robbery and apostasy are all punishable by death.
The interior ministry has cited deterrence as a reason for the punishments, but rights activists have raised concerns about the fairness of trials in the kingdom.
Read: First Saudi execution after Ramazan pause
Amnesty International says Saudi Arabia is one of the world's most prolific executioners, along with China, Iran, Iraq and the United States.
London-based Amnesty said the kingdom carried out a record 192 executions in 1995.
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