South African police said on Tuesday the death of a Nigerian man in custody late last ​month had nothing to do with a surge in ‌anti-migrant violence and that he collapsed after being arrested for drug possession.

Nigeria's foreign ministry alleged on Sunday the man had died ​during an interrogation by South African police two ​days before nationwide rallies against undocumented migrants, threatening unspecified action if ⁠there were more attacks on its citizens.

"The South African ​Police Service strongly rejects attempts to link this incident ​to anti-illegal immigrant protests," a police spokesperson said in a statement.

The spokesperson said a police drugs team had arrested the Nigerian at his ​apartment in an intelligence-driven operation. Drugs were found at ​the scene, and the man collapsed while being taken into custody ‌in ⁠a Pretoria police station, the spokesperson added.

Paramedics were called and declared him dead, and a police watchdog was notified and will investigate the incident, the spokesperson said.

South Africa's foreign ​ministry has said ​Nigeria's government ⁠should send in any evidence it has about the man's death but has not ​commented on the specific allegations made by its ​Nigerian ⁠counterpart.

The anti-migrant protests over the past few months have been mostly peaceful but at times turned violent, with attacks on ⁠foreign ​nationals and looting of foreign-owned shops.

Rights ​groups say foreigners are being used as scapegoats for deep-rooted problems like ​crime and unemployment.