(Reuters) -�Iran�and major powers were struggling on Monday to reach a preliminary nuclear accord as "gloom" set in, with both sides sticking to their positions a day before a self-imposed deadline.

For days�Iran, the United States, Britain,�France,�Germany,�Russia�and�China�have been trying to break an impasse in negotiations aimed at stopping Tehran having the capacity to develop a nuclear bomb, in exchange for an easing of�United Nations�sanctions that are crippling its�economy.

But officials at the talks in the Swiss city of Lausanne said attempts to reach a framework accord, which is intended as a prelude to a comprehensive agreement by the end of June, could yet fall apart.

Negotiators from all parties appeared increasingly pessimistic. "If we don't have some type of framework agreement now, it will be difficult to explain why we would be able to have one by June 30," said a Western diplomat.

He said three major sticking points must be resolved if�Iran�and the six powers are to secure the deal before March 31, and it is unclear whether those gaps could be filled.

The diplomat said the most difficult issues related to the duration of any limits on�Iranian uranium enrichment and research and development activities after an initial 10 years, the lifting of the sanctions and the restoring of them in case of non-compliance by�Iran.

"It seems that we have an accord for the first 10 years, but with regard to the Iranians the question of what happens after is complicated," the official said on condition of anonymity, adding: "I can't say what the final result will be."

German Foreign Minister Frank-Walter Steinmeier said there had been "some progress and some setbacks in the last hours".

By Reuters