Iran and six other countries led by the United States have reached a historic deal that President Obama says alters the pervading threat of Tehran's nuclear power usage in the future. However, the deal does nothing to prevent Iran from developing a nuclear weapon.

The agreement would eventually lift the economic sanctions set on Iran, diplomats who are engaged in the talks but are not authorized to speak have confirmed to Reuters, according to NBC News.

The formal announcement is set on Tuesday morning in Vienna, where the summit is being held.

The diplomat told Reuters that all the hard work done for more than two weeks has paid off for all. Iran and the P5+1 world powers - Russia, China, Britain, France, the U.S. and Germany - were members of the negotiating panel.

Part of the compromise reached is that Tehran will allow U.N. inspectors access to visits to Iranian military sites as part of their monitoring duties, the Associated Press reported.

However, Tehran included a condition that immediate access to any nuclear site without prior notice would not be granted. If Tehran's refusal for access to its nuclear facility is questioned by the United Nations, the former could demand for an arbitration board with representatives of the six countries led by the U.S. as members.

On the other hand, the positive results of the Iran nuclear deal have dragged down oil prices in the world market, Reuters said.

Oil prices led by Brent crude trading was down 1.7 percent at $57.85 a barrel at 7:30 a.m. London time, the report said.

Since Friday's deadline was missed, the U.S. Republican-led Congress will now have 60 days, rather than 30, to review a final accord. President Obama cannot waive sanctions on Iran until that congressional review is complete, according to AP.