(CNN) -- The U.S. State Department is advising Americans in South Africa to exercise extreme caution following the explosion earlier this week at a Planet Hollywood restaurant in Cape Town.

Although the restaurant is locally owned, it may have been targeted because of its American links, the State Department said, noting that there is a possibility of other such attacks.

Although the risk is probably highest in the Cape Town area, the State Department is advising Americans to exercise extreme caution in all urban areas of South Africa, particularly Durban, Pretoria and Johannesburg. U.S. citizens also are advised to avoid large crowds, demonstrations and other potentially volatile situations.