Hillary Rodham Clinton speaks to the crowd during a campaign rally at Transylvania University in Lexington, Kentucky, 19 May 2008

U.S. Senator Hillary Clinton has apologized for citing the 1968 assassination of presidential candidate Robert Kennedy while defending her decision to remain in the race for the White House.

The Democratic presidential candidate told reporters Friday that she meant no offense to the Kennedy family. She said she was trying to make the point that in 1968, candidates were still campaigning in June when Kennedy was killed.

Clinton made the comment while campaigning in South Dakota Friday. She said then that she could not understand calls for her to quit the race for her party's nomination when past Democratic races, such as Kennedy's, had extended into June.

Bill Burton, a spokesman for Clinton's Democratic rival, Senator Barack Obama, called the comment "unfortunate."

John McCain speaking to members of the National Restaurant Association in Chicago, 19 May 2008

Meanwhile, presumptive Republican presidential nominee John McCain released his medical records Friday to alleviate concerns about his well-being. Doctors say the senator is in "excellent health."

The records show McCain, who has had skin cancer, to be cancer-free and in good health.

If he wins in November, McCain would be the oldest person elected to a first term as U.S. president. The Arizona senator turns 72 in August.

Some information for this report was provided by AFP, AP and Reuters.