U.S. Marines stationed in southern Europe have been put on alert as a precaution in advance of expected large demonstrations and potential unrest in Egypt this weekend, CNN has learned.

President Barack Obama held a town hall meeting Saturday with a group of young people in the Soweto section of Johannesburg, with video links to similar groups in other cities in Africa.

At least three people were killed and 174 injured during clashes in Egypt on Sunday, officials said, exactly one year after the country's first democratically elected president came to power.

Andrew Pochter of Chevy Chase, Maryland, was stabbed Friday in the port city of Alexandria, Egypt. He was in the country teaching English to elementary school children.

The former wife of Nelson Mandela visited him Sunday in the hospital where the ailing anti-apartheid icon is clinging to life, the South African Press Association reported.

U.S. President Barack Obama wraps up his South Africa tour by visiting the prison where Nelson Mandela spent most of his time in detention.