Gerald Ford in hospital for tests

Gerald Ford became president in 1974 after Richard Nixon resigned

Former US President Gerald Ford has been taken to hospital in California for medical tests, his office has said.

It said Mr Ford, 93, was admitted to Eisenhower Medical Center in Rancho Mirage. However it did not disclose the nature of the tests.

"He is doing well. Updates will be provided at a later date," Mr Ford's spokeswoman Penny Circle said.

Mr Ford - who underwent heart surgery in August - has been in hospital at least three times already this year.

He remains the only US president never to have contested a national election before entering office.

As vice-president, he became president in 1974 when Richard Nixon resigned because of the Watergate affair.

But he failed to win a full term in the 1976 presidential election, losing to Democrat Jimmy Carter.

Mr Ford became the nation's oldest living former president after the death of Ronald Reagan in 2004.