JOHANNESBURG (AP) — The South African government says it is concerned about inflammatory remarks on social media following recent attacks on foreign immigrants.

Security officials said Wednesday that threatening posts, made by South Africans and immigrants against each other, have escalated. South African officials are appealing to people to refrain from remarks that could incite violence.

South African media say homes belonging to Nigerians were recently set on fire in neighborhoods of Johannesburg and Pretoria, the capital. Shops run by Somalis and Pakistanis were also looted.

Nigeria has urged the South African government to protect Nigerians and other African nationals currently in South Africa.

In 2015, anti-immigrant riots in and around the South Africa city of Durban killed at least six people. In 2008, similar violence killed about 60 people.