JOHANNESBURG, July 12 (Reuters) - South African police and the military have been deployed in several townships due to growing threats against foreign migrant workers and protests about squalid living conditions, police said on Monday.

Signs of social instability could harm South Africa's image and investor sentiment, undoing gains achieved by hosting the successful soccer World Cup tournament that ended on Sunday.

Police said they had arrested seven people and the situation in the Western Cape was tense but no one had been injured so far.

"There were two shacks that were burned in separate areas and there's been sporadic incidents of looting and threats have been made on foreign nationals," said Western Cape police spokesman Frederick van Wyk.

"Police have responded. At this moment there is a heavy police contingent (in several areas) which also includes Metro police and SANDF (South African National Defence Force)."

Sixteen years since the end of white minority rule, poor blacks are frustrated that their social conditions have not improved and the ruling African National Congress's promises of better housing, education and healthcare have not materialised.

South Africa has attracted millions of workers from across the continent and further afield, but they compete with local people for scarce jobs and resources. Two years ago more than 60 people were killed during anti-foreigner attacks.

Just a day after the World Cup ended, about 300 residents in Lenasia, south of Johannesburg, obstructed traffic with burning tyres and broken toilet seats, to protest about their living conditions. "Police have been deployed to the area and are trying to clear the crowds," said Wayne Minaar of the Johannesburg Metro Police Services.

Such protests, which were common before the World Cup, had died down during the 32-day soccer tournament. (Reporting by Phumza Macanda and Peroshni Govender; Editing by David Stamp)

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