Colombia's President Juan Manuel Santos speaks during a Presidential address in Bogota, Colombia, November 12, 2016. Colombian Presidency/Handout via REUTERS

BOGOTA (Reuters) - Colombian President Juan Manuel Santos said on Tuesday he will undertake medical tests in the United States this week for a possible return of prostate cancer.

Increased levels of prostate-specific antigen (PSA) were detected during a routine checkup and his doctor has recommended he travel as soon as possible for further tests, he told reporters.

Santos, 65, who won election in 2010 and is half-way through his second term, had successful surgery four years ago in Colombia to remove a tumor in his prostate.

“This news has taken me and my family by surprise. I will travel tomorrow, exams will take place on Thursday and I will return on Friday,” he said.

“I maintain confidence the results of these new exams will be positive,” he added, saying he would inform the nation of the outcome as soon as possible.

The Harvard-educated Santos, who won the Nobel Peace Prize last month for his efforts to end a half-century war with Marxist FARC rebels, spoke with his wife and doctor by his side.

The medical checks come at a busy time for the Colombian leader, as he tries to revive the FARC peace deal, which was rejected last month in a referendum, and also seeks to steer tricky tax reforms through parliament.

The tests will be carried out at the oncology center at Johns Hopkins Hospital in Baltimore.

PSA is a protein in the prostate gland and men with prostate cancer often have an elevated PSA.