South African companies with operations north of the border are suffering a fierce backlash from this week's wave of xenophobic violence, blamed on remarks by Zulu King Goodwill Zwelithini. On Friday, officials of the newly elected Nigerian government handed a memorandum to the South African high commission in that country, demanding that South Africa take swift action against the attackers - or else South African business in Nigeria would be shut down, news network eNCA reports.This will be of particular concern to MTN as Nigeria is the cellular giant's largest market, responsible for a third of its revenue for the year to December. MTN's share price shed 0.9% afterwards.On Friday, Chris Moroleng, MTN's head of corporate affairs, said none of its staff had been threatened.He said MTN was seen as a local rather than a South African company in most of its markets.Other companies with exposure to Nigeria - including Standard Bank, Nedbank, Shoprite, Sun International, Old Mutual, Naspers's MultiC hoice and Massmart - may yet feel the sting of this threat.Petrochemical giant Sasol was directly affected. It was forced to halt work at some of its projects in Mozambique.The group would evacuate 340 South Africans from Mozambique, Sasol spokesman Alex Anderson said on Friday."Mozambican employees of our service providers have expressed concern around the reported incidents of violence against Mozambicans and other foreign nationals in South Africa, and are also protesting about the presence of South African employees," he said.The border post between the two countries was closed on Friday after a Mozambican mob barricaded the N4 highway near Ressano Garcia, targeting trucks with South African registration numbers, according to the Corridor Gazette newspaper.Citizens in a number of African countries have vowed to retaliate, which puts several other South African companies at risk, including Barclays Africa, Vodacom and SABMiller.Earlier this week, Primedia CEO Roger Jardine said on social media that the corporate sector should act to mitigate the damage. "Can corporate South Africa expect to do business on the African continent yet be silent on xenophobia?" he asked.Gilbert Mutubuki, president of Zimbabwe's national students' union, allegedly incited Zimbabweans to attack South African students and businesses operating in his country.Within South Africa's borders, the attacks disrupted business.Nedbank this week shut down branches in Tongaat, Verulam, KwaMashu and Isipingo in KwaZulu-Natal.Nedbank said it has an "evacuation plan" for branches outside South Africa in place. Standard Bank would not discuss its contingency measures other than to say it was "working through these scenarios" .Jabu Khethe, the CEO of FNB International, said his bank remained "deeply committed" to expanding its African operations and opening in new countries...