US top diplomat John Kerry remains focused on nailing down a nuclear deal with Iran and plans to join the final negotiations in late June despite breaking his leg in a cycling accident, officials said Monday.

The globe-trotting Kerry landed in Boston from Geneva on a military C-17 plane accompanied by his personal doctor late Monday.

He then headed to Massachusetts General Hospital, and a surgical procedure to set his leg was scheduled for Tuesday morning, his spokesman John Kirby said.

His fall on Sunday in the French Alps comes as America juggles multiple foreign policy challenges, but was unlikely to derail the Iran talks, observers said.

The lanky 71-year-old, who is an experienced cyclist, broke his right femur on Sunday when his bike hit a curb as he started on a climb of a tricky, steep mountain pass near the French town of Chamonix.

Deputy State Department spokeswoman Marie Harf said Kerry was in "good spirits" Monday and had spoken to several European counterparts to apologize for cancelling stops in Madrid and Paris.

"He's committed to an aggressive, ambitious, and responsible recovery timeline," she told reporters.

"Look fwd to getting leg set & getting back to @StateDept!" Kerry said in a message on his Twitter account, using the hashtag #Onward.

Doctors told AFP that in such cases a patient could be up and walking within three to four days, and would be expected to make a full recovery in two months.

Prior to his surgical procedure, Kerry "will participate via telephone" in a conference on combating militants from the Islamic State (IS) group, which he had been scheduled to attend on Tuesday in Paris, Kirby said.

- Focus on Iran -

But all eyes are on the looming June deadline to reach a deal curtailing Iran's suspect nuclear program and end a 12-year standoff with the Islamic republic.

Even though the talks have involved a large American team, Kerry has over the past 18 months personally invested time and energy in the highly complicated negotiations, which could prove a lasting legacy of his tenure as secretary of state.

He has met many times with his Iranian counterpart Mohammad Javad Zarif, and the accident happened the day after six hours of "intense" talks in a Geneva hotel.

Even though their countries do not have diplomatic relations, the two men have got to know each other well, as they have tussled during tense all-night sessions chasing a deal.

"Secretary Kerry's main focus for the month of June remains squarely on the Iran negotiations. I want to be very clear about this. His injury does not change that," Harf told reporters.

"He and the entire team are absolutely committed to the same timetable and are working toward June 30th as the deadline for these talks."

But she acknowledged the logistics for future upcoming talks had not yet been finalized.

"Personal relationships matter, but I think what has held the talks together all this time has been a recognition that it is in the interests of both countries to get the nuclear issue resolved," said Alireza Nader, an international policy analyst with the Rand Corporation.

"The US team is pretty big and the US government has invested a lot of effort in this. I don't think the negotiations are necessarily dependent on one person."

Technical experts from the United States and Iran as well as Britain, China, France, Germany and Russia, have met almost continuously since an April 2 framework for a deal was laid down in Lausanne.

"Some of the issues that are now being discussed are probably some of the most difficult," Nader told AFP, highlighting there was still no agreement on lifting a network of sanctions against Iran or for inspecting its military sites.

- Recovery time -

Sam Barzideh, director of the Orthopaedic Fragility Fracture Service at Winthrop-University Hospital in New York, warned that since Kerry had a previous hip operation on the same leg his recovery could be complicated.

"A fracture needs to heal and that usually takes about two months," Barzideh told AFP, cautioning he was not privy to Kerry's medical records.

But he said the aim was to get the patient "to weight-bear as early as possible. The whole idea is for him to be able to walk the next day or within two to three days."