US Secretary of State John Kerry broke his right leg in an accident while cycling a portion of the Tour de France route near Scionzier, France, on Sunday and will remain in a Geneva hospital overnight for observation, his spokesman said.

Kerry, who cancelled visits to Madrid and Paris, initially planned to return to the United States later on Sunday.

"But after further consultation it was sensible for him to remain in the hospital for observation overnight for purely precautionary measures and fly home tomorrow," State Department spokesman John Kirby said in a statement.

Kirby added that Kerry "continues to be in great spirits and active," and had done a range of phone calls, including with President Barack Obama.

Kerry broke his femur but the injury is not life-threatening and he is expected to make a full recovery, Kirby said earlier. Kerry was taken to Geneva's main hospital and was in a stable condition.

He had been due later on Sunday to travel to Madrid, his first visit to Spain as secretary of state, to sign a bilateral defence agreement that would allow the United States to have permanent use of Moron air base, near Seville.

He had been scheduled on Monday to fly to Paris for a meeting with Iraqi Prime Minister Haidar al-Abadi and members of a U.S-supported coalition fighting the militant group Islamic State.

Kerry, 71, is still an avid sportsman and often takes his own bike on official trips abroad. The accident came the day after he met his Iranian counterpart, Mohammad Javad Zarif, in Geneva to try to overcome obstacles in negotiations on curbing Tehran's nuclear programme.

It was not immediately clear how his injury would affect the nuclear negotiations with just a month left before a June 30 deadline for a final agreement between Iran and the United States, Britain, France, Germany, Russia and China.

Kerry was flown by helicopter from the scene of the accident after he was stabilised by a doctor and paramedic who were with his accompanying motorcade.

A senior State Department official said it appeared Kerry had hit a curb. There was no vehicle involved.

Kerry was to return to his hometown of Boston for treatment at Massachusetts General Hospital. His plane and travelling party departed France ahead of Kerry, who was to take another plane outfitted to ensure his comfort as a precaution, Kirby said. – Reuters