U.S. Secretary of State John Kerry said on Sunday it was not up to Washington to set a deadline for Turkey and Israel to normalise ties but stressed the importance of restoring a full relationship between the two.

"It is not for the United States to be setting conditions or terms with respect to what the prime minister's (Tayyip Erdogan) schedule ought to be or what the requirements of Turkey are with respect to that process," Kerry said after arriving in Istanbul, his first stop on a 10-day trip to the Middle East, Europe and Asia.

"It is imperative that the compensation component ... of the arrangement be fulfilled, that the ambassadors be returned and that full relationship be embraced but it's not up to us to discuss the timing," Kerry told a news conference.

On the other hand, Kerry said major powers would continue talks with Iran to resolve a decade-old dispute over Tehran's nuclear programme, but stressed the process could not continue for ever. "This is not an interminable process," said Kerry.

He said US President Barack Obama was committed to continuing the diplomatic process despite what he called the complicating factor of Iranian elections in June.

"Diplomacy is a painful task," he noted. "And a task for the patient."

Talks between Iran and the powers ended in Kazakhstan on Saturday after failing to break a deadlock. No new talks were scheduled.