US Secretary of State John Kerry says he is “hopeful” to reach a nuclear deal with Tehran after a “very good meeting” with Iranian Foreign Minister Mohammad Javad Zarif.

"I think we're getting to some real decisions. So I will say, because we have a few tough things to do, I remain hopeful. Hopeful," he said.

Kerry’s statement comes only one day before the Monday deadline for a possible nuclear deal between Iran and the P5+1 group of countries.

The nuclear negotiations have entered the 16th day after missing the initial deadline of June 31.

Russian Foreign Minister Sergei Lavrov is set to join the foreign ministers of the rest of the P5+1 group of countries later on Sunday.

In a weekend speech, Kerry told reporters that although the negotiating parties “will not rush or be rushed” to a deal, the negotiations are not meant to go on forever.

Kerry stated that despite progress in talks, there are still tough issues that remain to be resolved.

One of those issues is the unlimited inspections of Iranian military sites which Tehran insists are off the table.

Tehran has also urged a new UN Security Council resolution that will make all the previous resolutions against its peaceful nuclear program illegal.

Earlier, Zarif made it clear that the West must choose between agreement or coercion. He also blamed the West for the slow progress made during the course of the talks, saying “now, they have excessive demands.”