Kerry was to fly in from London on the last stop of his latest diplomatic trip, to brief his French, German and British counterparts on the negotiations.
The top US diplomat spent three days in Switzerland earlier this week huddled with Iranian Foreign Minister Mohammad Javad Zarif seeking to hammer out a deal as a March 31 deadline looms.
But French Foreign Minister Laurent Fabius, who will meet first with Kerry for bilateral talks today, remained sceptical.
Fabius gave no figures but key issues in the talks which began in late 2013 include the level of uranium enrichment that Iran should be allowed, the degree of international oversight of its programme and how long an accord should last.
"The deadline is March 31 but in the event it could be later, although everyone wants to make progress by the end of the month," Fabius said.
"We are seeking to show that Iran's program is exclusively peaceful and that we can block all of the pathways necessary to acquire the fissile material for a nuclear weapon and then to be able to move towards the production of that weapon," Kerry said on Thursday after briefing Gulf foreign ministers in Riyadh on the state of the talks.
"To date, we have made progress, but there do remain serious gaps, and those need to be resolved," he stressed.
Bilateral negotiations between the US and Iran will resume on March 15.
Further talks between the group known as the P5+1 -- Britain, China, France, Germany, Russia and the United States -- and Tehran are also expected.
"We expect soon thereafter to know whether Iran will, in fact, be able to make the tough decisions that are required to get where we need to be," Kerry said.
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