Iran and six major powers have reached a historic nuclear deal, which will grant Tehran sanctions relief in exchange for curbs on its nuclear programme, an Iranian diplomat said on Tuesday.

"All the hard work has paid off and we sealed a deal. God bless our people," the diplomat told Reuters on condition of anonymity. Another Iranian official confirmed the agreement.

The foreign ministers of Iran and six major powers will meet for nuclear talks at 0830 GMT at the United Nations centre in Vienna to be followed by a news conference, a spokeswoman for the European Union said on Tuesday.

Tehran and the six powers have been holding marathon diplomatic negotiations at the ministerial level for more than two weeks to resolve a 12-year stand-off over Iran's nuclear programme.

Meanwhile, Reuters reported that a draft nuclear deal between Iran and six major powers calls for UN inspectors to have access to all suspect Iranian sites, including military.

The source also said that if the deal is agreed, 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 programme and relief from sanctions on Iran - implemented in the first half of 2016.

The information from the source was preliminary and subject to change as 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. - Reuters