By Louis Charbonneau and Fredrik Dahl
VIENNA (Reuters) - Negotiators from Iran and six world powers struggled on Wednesday to narrow "significant gaps" in talks aimed at clearing the way for a long-term accord on curbing Tehran's nuclear program.
The negotiators from Iran and the so-called P5-plus-one - the United States, Russia, China, Britain, France and Germany - plan after their two days of talks in Vienna to start drafting the agreement to meet a self-imposed July 20 deadline.
"The Iranians clearly have a sense of urgency to get a deal done, as does the P5+1," a Western diplomat close to the talks told Reuters.
"We know that there are still some significant gaps that remain and know this process will not be easy. But we're all committed to getting it (the draft) done by July 20," he said, in an assessment echoed by other Western diplomats.
The toughest areas to be tackled are Iran's future uranium enrichment capacity, nuclear facilities that Western powers believe have little or no civilian value, and future nuclear research work, as well as a schedule of steps to remove the international sanctions that have crippled Iran's economy.
Background tensions over Russia's involvement in Ukraine and Western threats of further sanctions against Moscow and over the U.S. denial of a visa for Iran's proposed new U.N. envoy in New York have so far not harmed the nuclear talks, diplomats say.
A senior Iranian official said Tehran was seeking to protect its "red lines" in what he said were "difficult" negotiations.
"Iran wants a deal in which its rights have been considered," the official said. "The talks have entered a very difficult stage. Making progress is difficult."
The six powers' goal is to extend the "breakout" period Iran would need to develop an atomic weapon as much as possible. U.S. Secretary of State John Kerry said on Tuesday the current Western view of that period is two months.
Iran's Supreme Leader Ayatollah Ali Khamenei has repeatedly said that the oil-producing OPEC member's "red lines" are that it will never give up enrichment or shut any nuclear facility.
Among the toughest issues are Iran's centrifuge research and development program, the size of its uranium stockpiles, the future of the Arak research reactor that could eventually yield significant quantities of bomb-grade plutonium, and the future of the previously hidden Fordow underground enrichment plant.
The stakes are high. Western powers, along with Russia and China, want to avert an escalation of tensions in the Middle East in the form of a new war or a regional nuclear arms race.
Iran, which denies accusations it is seeking a nuclear weapons capability, wants an end to sanctions and to regain what it sees as its rightful place as a leading regional power.
The current Vienna talks are building on a preliminary deal that Iran and the six powers reached in Geneva last November.
(Additional reporting by Parisa Hafezi, Fredrik Dahl and Justyna Pawlak; Editing by Gareth Jones)