A draft nuclear deal between Iran and six major powers calls for United Nations inspectors to have access to all suspect Iranian sites, including military, based on consultations between the powers and Tehran, a diplomatic source said on Tuesday (Vienna time).

The source also said that if the deal is accepted, a UN Security Council resolution on it would ideally be adopted this month and the steps to be taken by both sides - including Iranian limitations on its nuclear program and relief from sanctions on Iran - would be implemented in the first half of 2016.

The information from the source was preliminary and subject to change because it was based on a draft of the nuclear deal that was not the final version and that could be amended before final approval by Iran and the six powers.

Meanwhile, Iran and the six nations (the United States, Britain, Russia, France, and China plus Germany) are scheduled to hold a comprehensive meeting at 4 a.m. Eastern time Tuesday to discuss a possible final nuclear deal, which will curb the country's nuclear work in exchange for lifting sanctions, the semi-official Fars news agency reported.

Diplomats close to the talks say that they are hoping to approve a final version of the draft document as early as Tuesday. Negotiations were continuing in the early hours of Tuesday to reach an agreement, the diplomats said.

The source said that Iran and the UN International Atomic Energy Agency have agreed on a plan to address outstanding questions about the possible military dimensions of past Iranian nuclear activity by the end of this year, adding that some sanctions relief would be conditioned on Tehran resolving this issue.

The plan agreed by the IAEA and Iran includes one visit to the Parchin military site as well as possible interviews with Iranian nuclear scientists, the source noted.

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Nuclear negotiations between Tehran and six world powers missed a midnight deadline on Monday to reach a final deal, but diplomats from all sides said they hoped for a breakthrough in the coming hours.

The details of the draft deal, which is still being negotiated, are broadly in line with an interim agreement clinched on April 2 in Lausanne, Switzerland.